Liquid crystal display device and associated fabrication method

ABSTRACT

In a liquid crystal display device which displays images by changing light transmission through formation of a bend alignment state of the liquid crystal, a large pretilt angle domain is formed on at least either the surface of the pixel electrode or the surface of the counter electrode and the large pretilt angle domain is so conditioned as to cause a larger pretilt angle of the liquid crystal molecules than the surrounding region does. This permits quick, reliable transition from a splay alignment state to the bend alignment state. Such transition is also facilitated by adding a chiral agent to a liquid crystal. A combination of the large pretilt angle domain and a chiral agent further facilitates occurrence of the transition.  
     Another liquid crystal display device is designed such that the twist angle of the molecules of the liquid crystal ranges from  160°  to  200°  and that the fast response achieved by formation of an alignment state similar to the bend alignment state can be achieved without formation of the bend alignment state. by applying a driving voltage higher than the voltage, which causes the extremum of transmission in the driving voltage-transmission characteristic of the device, between the pixel and counter electrodes.  
     In another liquid crystal display device, the pixels corresponding to the pixel electrode are divided into at least two domains which cause bend director fields having different orientations, thereby improving viewing angles.  
     In still another liquid crystal display device, the twist angle of the molecules of the liquid crystal is in the range of from  160°  to  200°  or from  250°  to  290°  and the liquid crystal layer contains a dye or pigment. The device is driven with voltages in a certain high range. With this arrangement, the difficulty in causing the transition can be overcome.  
     Another liquid crystal display device has pretilt angles varying according to the colors of pixels. This arrangement prevents hue shifts caused by changes in the transmission of the liquid crystal, the changes being due to the different wavelengths of transmitted light.

BACKGROUND OF THE INVENTION

[0001] (1) Field of the Invention

[0002] The invention relates to liquid crystal display devices wellsuited for use in computer displays, television receivers and otherindustrial products and to methods for fabricating them. Moreparticularly, the invention pertains to light-transmissive type andlight-reflective type liquid crystal display devices capable ofproviding rapid response and a wide range of viewing angles and tofabrication methods thereof.

[0003] (2) Description of the Related Art

[0004] There have been practically used twisted-nematic (TN) liquidcrystal display devices incorporating a nematic liquid crystal. The TNmode, however,-has the drawback of poor response. Another disadvantageof the TN mode is that viewing angles, that is, angles through which theviewer can see images properly are narrow. Concretely, when diagonallyviewing images in a TN liquid crystal display device, brightness andcontrast decrease and gray scale inversion occurs. For this reason, suchTN mode is unacceptable for liquid crystal display systems-which operateat high speed to provide animatic images or require good angularviewability when viewed in diagonal directions. Another known type ofliquid crystal display devices is the Polymer Dispersed Liquid Crystal(PDLC) mode that utilizes the effect of light dispersion. This modeadvantageously provides high brightness, because it does not require useof a polarizing plate. However, the response speed of the PDLC mode isas low as that of TN liquid crystal display devices. Additionally, thePDLC mode provides a wide range of viewing angles but the viewing anglesof the PDLC mode cannot be controlled in principle by a phasecompensating layer like the TN mode. There have been developed othertypes of liquid crystal display devices: Ferroelectric Liquid Crystal(FLC) and Anti-Ferroelectric Liquid Crystal (AFLC) These modes sufferfrom the critical problems of poor shock resistance and temperaturecharacteristics and therefore have not been put to practical use.

[0005] In attempt to overcome the foregoing problems, OpticallyCompensated Bend (OCB) liquid crystal display devices have beenproposed, which exhibit extremely rapid response and a relatively widerange of viewing angles. One example of such devices is disclosed inJapanese Patent Laid-Open Publication No. 7-84254 (1995). One embodimentof the OCB liquid crystal display devices according to this publicationis designed as shown in FIG. 1 to have a liquid crystal cell 11 in whicha liquid crystal 12 is enclosed between a pair of transparent substrates13, 14 and in which a pixel electrode 15, a counter electrode 16 andalignment films 17, 18 are formed on the transparent substrates 13, 14.The surfaces of the alignment films 17, 18 are conditioned so as to forma bend alignment state in which liquid crystal molecules 12 a, 12 bproximate to or contacting the alignment films 17, 18 are symmetricallytilted as shown in FIG. 1. More concretely, the surfaces of thealignment films 17, 18 are rubbed in the same direction to form apretilt angle ranging from several degrees to 10 degrees. The bendalignment state may include twist in the proximity of the centers of thetransparent substrates 13, 14 (i.e., liquid crystal molecules in theproximity of the centers are twisted so that they do not lie in theplane where X and Z axes lie) depending on design conditions. Providedon both sides of the liquid crystal cell 11 are polarizing plates 19,20. Sandwiched between the transparent substrate 14 and the polarizingplate 20 is a phase compensating layer 21 for optically compensating thedirector alignment of the liquid crystal 12. In the above-described bendalignment state, the liquid crystal molecules change rapidly with achange in the driving voltage applied between the pixel electrode 15 andthe counter electrode 16, and consequently, fast response can beachieved. Such fast response due to the rapid molecular change can beobtained even when changing applied voltage between two levelscorresponding two halftones which have a slight difference inbrightness. The symmetry of the bend alignment state increases theangular viewability in the plane where X and Z axes lie so that e.g., aviewing angle of about ±50° can be achieved, whereas the phasecompensating layer 21 increases angular viewability in the plane where Yand Z axes lie so that e.g., a viewing angle of about ±40° can beachieved. Note that, in FIG. 1, X and Y axes designate the transversedirection and vertical direction, respectively, of the display screen.The phase compensating layer 21 also contributes to a reduction indriving voltage.

[0006] The OCB liquid crystal display device presents a difficultproblem. That is, it requires formation of the bend alignment stateprior to image displaying, which is unfavorable for the followingreason. When no voltage is applied between the pixel electrode 15 andthe counter electrode 16, the bend alignment state is not formed but asplay alignment state P with the liquid crystal molecules arrangedfanwise is created as shown in FIG. 2, even if the above surfacetreatment is applied to the alignment films 17, 18. Therefore, at thetime such as when a power supply is turned on, the splay alignment stateP should be changed to the bend alignment state Q by application of highelectric energy. The transition from the splay alignment state P to thebend alignment state Q can be caused at relatively high speeds byapplying a comparatively high voltage ranging from e.g., 10V to 30Vbetween the pixel electrode 15 and the counter electrode 16. However, ittakes more than tens of minutes to cause the transition when applying avoltage (several volts) which is low enough to avoid excessive load onthe driving ICs. In the worst case, such transition does not occur afteran elapse of more than one hour. This hinders practical use of the OCBliquid crystal display device.

[0007] As an attempt to solve the above problem, Japanese PatentLaid-Open Publication No. 9-96790 (1997) proposes a technique in whichthe twisted alignment of the liquid crystal molecules as seen in the TNmode is combined with the rising alignment (in which the liquid crystalmolecules are aligned in a direction normal to the substrates) similarto that of the OCB mode. This technique is intended to solve the aboveproblem by eliminating the need for formation of the bend alignmentstate and to achieve higher response speed than the TN mode by forming adirector alignment similar to the bend alignment state. In reality,however, fast response can not be necessarily achieved even if adirector alignment similar to the bend alignment state is formed.

[0008] Although the above prior art OCB liquid crystal display devicesucceeds in providing wide viewing angles to a certain extent, it stillhas difficulty in largely increasing the viewing angle within the planewhere Y and Z axes lie (see FIG. 1) by the phase compensating layer 21alone and therefore the viewing angle characteristics vary significantlyaccording to viewing directions. Accordingly, the OCB liquid crystaldisplay device leaves much to be desired in the viewing angleuniformity. As mentioned earlier, the viewing angle within the planewhere X and Z axes lie (FIG. 1) can be improved by the symmetry of thebend alignment state. In order to further increase the viewing anglesnot only in this direction but also in other directions, it isconceivable to use a biaxial phase compensating layer as the phasecompensating layer 21. However, the fabrication of such a phasecompensating layer requires accurate control of index of refraction intriaxial directions, so that where the OCB liquid crystal display deviceis applied to a large screen display system, it is extremely difficultto form such a compensating layer that posses uniform propertiesthroughout the display screen.

[0009] In many cases, the polarizing plates 19, 20 are placed as shownin FIG. 3 such that their polarization axes respectively form an angleof 45° or a specified angle relative to the conditioning direction ofthe alignment films 17, 18. In this case, light incident on the liquidcrystal cell 11 passes through the liquid crystal 12 in thebirefringence mode. Such propagation tends to cause the viewing angledependence of the hues of a display image (i.e., hues and colorstability may vary according to viewing angles). Hue shifts would becaused not only by certain viewing angles but also by the followingfactors even when images are viewed squarely (i.e., in a directionperpendicular to the substrates). FIG. 4 shows the transmission rates ofblue, green and red light where different voltages are applied betweenthe pixel and counter electrodes of a liquid crystal display device. Theliquid crystal display device used herein is produced under thefollowing conditions:

[0010] Alignment film: Polyinide director alignment film PSI-A2204produced by Chisso Corporation.

[0011] Liquid crystal: MT-5540 produced by Chisso Corporation.

[0012] Phase compensating layer: Biaxial oriented film produced by NittoDenko Corporation.

[0013] Gap distance of a liquid crystal cell: about 5 μm

[0014] Pretilt angle: 5° to 6°

[0015] Other conditions:

[0016] (1) The upper and lower substrates are bonded such that therubbing directions of the alignment films are parallel to each other.

[0017] (2) Wavelengths at the centers of the spectra of blue, green andred light are approximately 450 nm, 540 nm and 630 nm, respectively.

[0018] As shown in FIG. 4, the light transmission of the liquid crystalvaries according to the wavelength of transmitted light. Moreconcretely, when a voltage of 2V is applied between the pixel andcounter electrodes, the transmission rates of blue, green, red light are0.08, 0.045 and 0.025, respectively. Accordingly, entire images on thescreen become bluish. Although it is conceivable that hue shifts can beprevented by adjusting the voltage applied between the pixel and counterelectrodes according to the color of light, such adjustment leads to anincreased scale of the circuit and a higher production cost.

SUMMARY OF THE INVENTION

[0019] According to the first aspect of the invention, there is provideda liquid crystal display device comprising (1) a pixel electrode, (2) acounter electrode and (3) a liquid crystal enclosed between the pixeland counter electrodes,

[0020] wherein the respective opposed surfaces of the pixel and counterelectrodes are conditioned such that liquid crystal molecules contactingor in the vicinity of the surfaces have specified pretilt angles,

[0021] wherein images are displayed by changing light transmissionthrough formation of a bend alignment state of the liquid crystal, and

[0022] wherein a large pretilt angle domain is formed on at least eitherone of the surfaces of the pixel and counter electrodes, the largepretilt angle domain causing a larger pretilt angle of liquid crystalmolecules than a region surrounding the large pretilt angle domain does.

[0023] One of the objects of the invention is to quickly and reliablycarry out the transition from the splay alignment state to the bendalignment state in a liquid crystal display device which displays imagesby changing light transmission through formation of the bend alignmentstate of the liquid crystal.

[0024] To accomplish this object, a liquid crystal display deviceaccording to the invention includes a large pretilt angle domain whichis formed on at least either the surface of the pixel electrode or thesurface of the counter electrode and which is conditioned such that thepretilt angle of liquid crystal molecules caused by the large pretiltangle domain is larger than the pretilt angle of molecules caused by theregion surrounding the large pretilt angle domain. The liquid crystalmolecules proximate to or contacting the large pretilt angle domain arecomparatively raised, and therefore become a core for the transitionfrom the splay alignment state to the bend alignment state when voltageis applied between the pixel electrode and the counter electrode. Withthis core, the transition region grows and expands, which enables thetransition to occur reliably throughout the liquid crystal in a shorttime. In addition, such transition does not consume large amounts ofelectric energy so that the driver circuit is not subjected to excessiveload.

[0025] To achieve the inventive effect, that is, the rapid, reliabletransition, we tried to clarify the mechanism of the transition of thedirector alignment state After a rigorous study, we found that justafter application of voltage, the transition was more likely to occur inthe vicinity of spacers which were disposed irregularly between thetransparent substrates in order to keep a constant gap between thetransparent substrates. The reason for this is that the alignment of theliquid crystal molecules proximate to the spacers tends to be irregularunder the influence of the configuration of the spacers and otherphysical properties of their surfaces so that some molecules near thespacers have larger tilt angles than the tilt angle of the molecules farfrom the spacers. Such molecules triggers an occurrence of thetransition from the splay alignment state to the bend alignment state inthe neighborhood of the spacers. However, such transition is accidentaland therefore does not occur in the neighborhood of every spacer.Moreover, the spacers may shift and are not necessarily positioned onall the pixels. Liquid crystal display devices usually have a multitudeof pixels, and if parts of the pixels do not have such transition, soundimages cannot be displayed. To solve this problem and achieve thehigh-speed, reliable transition, we have come to the idea of theprovision of the large pretilt angle domain. Such a large pretilt angledomain may be formed, for example, by partially applying an alignmentfilm material, which imparts a large pretilt angle to liquid crystalmolecules, to the surface of an electrode, through phase separation orprinting. Alternatively, it may be formed by providing a smallprojection on an electrode.

[0026] According to the second aspect of the invention, there isprovided a liquid crystal display device comprising (1) a pixelelectrode, (2) a counter electrode, (3) a liquid crystal enclosedbetween the pixel and counter electrodes, and (4) a phase compensatinglayer, wherein images are displayed by changing light transmissionthrough formation of a bend alignment state of the liquid crystal andwherein the liquid crystal contains a chiral agent.

[0027] The above-described transition can be easily induced by adding achiral agent to the liquid crystal. A combination of the large pretiltangle domain and the chiral additive causes the transition more easily.

[0028] According to the third aspect of the invention, there is provideda liquid crystal display device comprising (1) a first substrate havinga pixel electrode formed thereon, (2) a second substrate having acounter electrode formed thereon and positioned opposite the firstsubstrate, (3) a liquid crystal enclosed between the first and secondsubstrates, (4) a first polarizer and a second polarizer disposed so asto sandwich the first and second substrates, the polarizing axes of thefirst and second polarizers crossing at right angles, and (5) a drivercircuit for applying driving voltage between the pixel electrode and thecounter electrode,

[0029] wherein the liquid crystal molecules of the liquid crystal have atwist angle ranging from 160° to 200°, and

[0030] wherein the driver circuit applies driving voltage between thepixel and counter electrodes, the driving voltage being higher than thehighest one of voltages that cause the maximal value of lighttransmission in the driving voltage-transmission characteristic of theliquid crystal display device.

[0031] According to the above liquid crystal display device of theinvention, the twist angle of the molecules of the liquid crystal is inthe range of from 160° to 200°, and a voltage higher than the voltagethat causes the extremum (maximal or minimal value) of lighttransmission in the driving voltage-transmission characteristic of theliquid crystal display device is applied between the pixel electrode andthe counter electrode. With this arrangement, response as fast as thatachieved by a device which forms the bend alignment state can beachieved without forming an alignment state similar to the bendalignment state. Concretely, since the liquid crystal molecules are keptin a twisted condition in the above device, there is no need to make adiscrete-phase transition such as the transition from the splayalignment state to the bend alignment state. Additionally, the liquidcrystal molecules can be brought into an alignment state similar to thebend alignment state by application of the above-specified voltage. Byvirtue of this, images can be displayed, for instance, just afterturning on the power supply of the liquid crystal display device andexcellent response can be ensured.

[0032] According to the forth aspect of the invention, there is provideda liquid crystal display device comprising (1) a pixel electrode, (2) acounter electrode and (3) a liquid crystal enclosed between the pixeland counter electrodes,

[0033] wherein images are displayed by changing light transmissionthrough formation of a bend alignment state of the liquid crystal, and

[0034] wherein pixels corresponding to the pixel electrode are dividedinto at least two domains which cause bend director fields havingdifferent orientations in the liquid crystal.

[0035] To improve viewing angle characteristics, thereby achieving goodviewability in various directions in a liquid crystal display devicewhich displays images by changing light transmission through formationof the bend alignment state of liquid crystal molecules, pixelscorresponding to the pixel electrode are divided into at least twodomains which cause bend director fields having different orientationsin the liquid crystal. Such domain division can be accomplished byrubbing a plurality of regions on the alignment films in differentdirections or alternatively, by directing ultraviolet rays havingdifferent polarizing or illuminating directions onto the regions. Withthis arrangement, the self compensating ability of viewing anglesinherent in the bend director alignment is exerted in a plurality ofdifferent directions so that good viewability in various directions canbe ensured. Further, a phase compensator may be used in conjunction withthe above arrangement to improve the viewing angle characteristics.

[0036] According to the fifth aspect of the invention, there is provideda liquid crystal display device comprising (1) a twisted liquid crystalcell having a liquid crystal layer sandwiched between a pair ofsubstrates, the liquid crystal layer having liquid crystal moleculestwisted between said pair of substrates and (2) a polarizing platedisposed on either the light incoming side or light outgoing side of theliquid crystal cell,

[0037] wherein said polarizing plate is disposed such that itspolarizing axis is substantially parallel to the longitudinal axis ofthe liquid crystal molecules on the interface of one of said pair ofsubstrates, said substrate being on the light incoming side or lightoutgoing side,

[0038] wherein the twist angle of the liquid crystal molecules in saidliquid crystal layer is in the range of from 160° to 200° and saidliquid crystal layer contains a dye or pigment,

[0039] which has a voltage-brightness characteristic according to whichwhen the voltage applied to said liquid crystal cell exceeds theFreedericksz threshold voltage of the liquid crystal, brightness firstrises gently with a first gradient and then rises with a second gradientsharper than the first gradient, and

[0040] which performs image displaying with applied voltages at leasthigher than the voltage corresponding to the turning point wherebrightness changes from the first gradient to the second gradient.

[0041] To solve the problems of (i) the difficulty in causing thetransition from the splay alignment state to the bend alignment state,(ii) the difficulty in fabricating a phase compensator of excellentproperties for improving the viewing angles and (iii) the viewing angledependence of hues which results in hue variation and color instabilityaccording to viewing angles, the twist angle of the liquid crystalmolecules should be in the range of from 160° to 200° or from 250° to290°, the liquid crystal layer should contain a dye or pigment, andimage displaying is performed with driving voltage falling within aspecified high range. According to the above arrangement, since theliquid crystal layer contains a dye or pigment, this liquid crystaldisplay device utilizes the guest-host effect. therefore, the aboveliquid crystal display device can overcome the viewing angle dependenceof hues that is one of the outstanding problems imposed by theconventional OCB liquid crystal display devices incorporating thebirefringence mode. In addition, the above display device is not thebirefringence mode, there is no need to include a phase compensatinglayer. Use of the twisted liquid crystal cells enables it to displayimages without the transition from the splay alignment state to the bendalignment state. Image displaying with driving voltage in a specifiedhigh range permits fast response and a satisfactorily high contrast.

[0042] According to the sixth aspect of the invention, there is provideda liquid crystal display device comprising (1) a plurality of pixelelectrodes constituting a plurality of pixels, (2) a counter electrode,(3) a liquid crystal enclosed between the pixel electrodes and thecounter electrode, and (4) a color filter having regions respectivelycorresponding to said pixels, each region transmitting any one of aplurality of colors,

[0043] wherein at least either the surfaces of the pixel electrodes orthe surface of the counter electrode is conditioned such that liquidcrystal molecules in the vicinity of the surfaces or surface are alignedso as to form specified pretilt angles,

[0044] wherein images are displayed by changing light transmissionthrough formation of a bend alignment state of said liquid crystal, and

[0045] wherein said specified pretilt angles vary according to thecolors of the pixels.

[0046] In the above liquid crystal display device, hue shifts caused bythe dependence of the transmission of the liquid crystal on thewavelength of transmitted light can be overcome by setting pretiltangles according to the colors of the pixels. Specifically, differentpretilt angles are formed for the three primary colors so that the samevoltage-transmission characteristic can be attained for the threeprimary colors.

BRIEF DESCRIPTION OF THE DRAWINGS

[0047]FIG. 1 is a longitudinal sectional view showing the structure of aprior art liquid crystal display device

[0048]FIG. 2 is a longitudinal sectional view showing the structure ofanother prior art liquid crystal display device.

[0049]FIG. 3 is a diagram of the orientations of optical elements of aliquid crystal display device.

[0050]FIG. 4 shows the transmission-applied voltage characteristic ofanother prior art liquid crystal display device.

[0051]FIG. 5 is a longitudinal sectional view showing the structure of aliquid crystal display device according to first, second, thirdembodiments of the invention.

[0052]FIG. 6 is a longitudinal sectional view showing the structure of aliquid crystal display device according to a forth embodiment of theinvention.

[0053]FIG. 7 is a longitudinal sectional view showing the structure of aliquid crystal display device according to a fifth embodiment of theinvention.

[0054]FIG. 8 is a longitudinal sectional view showing the structure of aliquid crystal display device according to a seventh embodiment of theinvention.

[0055]FIG. 9 is a diagram of the orientations of optical elements of theliquid crystal display device according to the seventh embodiment.

[0056]FIG. 10 shows the voltage-transmission characteristic of theliquid crystal display device according to the seventh embodiment.

[0057]FIG. 11 shows the voltage-transmission characteristic of theliquid crystal display device according to an eighth embodiment of theinvention.

[0058]FIG. 12 is a diagram of the orientations of optical elements ofthe liquid crystal display device according to a ninth embodiment of theinvention.

[0059]FIG. 13 shows the voltage-transmission characteristic of theliquid crystal display device according to the ninth embodiment.

[0060]FIG. 14 is a longitudinal sectional view showing the structure ofa liquid crystal display device according to a tenth embodiment of theinvention.

[0061]FIG. 15 is a partially sectional top view showing the structure ofthe liquid crystal display device according to the tenth embodiment.

[0062]FIG. 16 is a longitudinal sectional view showing the structure ofa liquid crystal display device according to an eleventh embodiment ofthe invention.

[0063]FIG. 17 shows a surface alignment technique according to a twelfthembodiment of the invention.

[0064]FIG. 18 is a sectional view of a liquid crystal display device Caccording to a thirteenth embodiment of the invention.

[0065]FIG. 19 shows the orientations of optical elements of the liquidcrystal display device C according to the thirteenth embodiment.

[0066]FIG. 20 shows the voltage-transmission characteristic of theliquid crystal display device C according to the thirteenth embodiment.

[0067]FIG. 21 is a partially enlarged view corresponding to FIG. 20.

[0068]FIG. 22 shows the voltage-transmission characteristic of a liquidcrystal display device E4 according to a fifteenth embodiment of theinvention.

[0069]FIG. 23 is a partially enlarged view corresponding to FIG. 22.

[0070]FIG. 24 shows the tilt angle of directors in the liquid crystaldisplay device C, the tilt angle being obtained from simulation.

[0071]FIG. 25 shows the orientation of directors in the liquid crystaldisplay device C, the orientation being obtained from simulation.

[0072]FIG. 26 shows the relationship between the tilt angle of directorsand applied voltage in the liquid crystal display device C.

[0073]FIG. 27 shows the tilt angle of directors in the liquid crystaldisplay device E4, the tilt angle being obtained from simulation.

[0074]FIG. 28 shows the orientation of directors in the liquid crystaldisplay device E4, the orientation being obtained from simulation.

[0075]FIG. 29 shows the relationship between the tilt angle of directorsand applied voltage in the liquid crystal display device E4.

[0076]FIG. 30 shows the orientations of optical elements of a liquidcrystal display device F according to an eighteenth embodiment of theinvention.

[0077]FIG. 31 shows the voltage-brightness characteristic of the liquidcrystal display device F according to the eighteenth embodiment.

[0078]FIG. 32 shows the viewing-angle characteristics of the liquidcrystal display device F according to the eighteenth embodiment.

[0079]FIG. 33 is a sectional view of a liquid crystal display device Gaccording to a nineteenth embodiment of the invention.

[0080]FIG. 34 shows the transmission-applied voltage characteristic of aliquid crystal display device according to a twentieth embodiment of theinvention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0081] [Embodiment 1]

[0082] Now there will be explained one example of OCB liquid crystaldisplay devices, in which the transition from the splay alignment stateto the bend alignment state quickly occurs. Referring to FIG. 5, aliquid crystal cell 38 that constitutes a liquid crystal display devicehas transparent substrates 33, 36 made of glass, between which a nematicliquid crystal 37 (“ZLI-47920” produced by Merck KGaA) having positivedielectric anisotropy is enclosed. The transparent substrate 33 hastransparent pixel electrodes 31 and an alignment film 32 formed thereon,whereas the transparent substrate 36 has a counter electrode 34 and analignment film 35 formed thereon. Spherical spacers 51 each having adiameter of about 6 μm mare interposed between the transparentsubstrates 33 and 36 whereby the gap distance between the substrates 33,36 can be kept constant. Disposed on both sides of the liquid crystalcell 38 are polarizing plates 39, 40. Between the transparent substrate36 and the polarizing plate 40 is a phase compensator 43. Eachtransparent pixel electrode 31 is, for instance, in the form of a 100μm×300 μm rectangle. While there are shown only three pixels in FIG. 5,a plurality of such pixel electrodes are provided in an actual displaydevice to display bit map images. Large pretilt angle domains 32 h, 35 hare formed on the alignment films 32, 35, respectively, and morespecifically, at least one domain 32 h or 35 h is formed for each pixel.The alignment films 32, 35 are conditioned in the same direction. Withthis arrangement, when no voltage is applied to the liquid crystal cell38, liquid crystal molecules are arranged in a splay alignment state,and when a specified voltage is applied, they are arranged in a bendalignment state. The process of the surface treatment applied to thealignment films 32, 35 is as follows.

[0083] (1) For forming a small pretilt angle, a polyimide surfacealignment agent of the polyamic acid type, which is capable of forming apretilt angle of about 5° and commercially available from NissanChemical Industries Ltd. under the number SE-7492, is used. For forminga large pretilt angle, a polyimide surface alignment agent of theprepolymerized type, which is capable of forming a pretilt angle ofabout 15° and commercially available from Japan Synthetic Rubber Co.,Ltd. under the number JALS-246 is used. 100 parts of the former agentand 10 parts of the latter agent are mixed. The mixture is applied tothe transparent pixel electrodes 31 and the counter electrode 34, andthen dried and sintered to form the director alignment films 32, 35.During the drying process, the two surface alignment agents undergophase separation so that the large pretilt angle domains 32 h, 35 h areformed.

[0084] (2) The entire surfaces of the alignment films 32, 35 are treatedby rubbing, using, for example, a rubbing cloth made of rayon, so thatthe above large and small pretilt angles are attained.

[0085] A voltage of 8V was applied by a driver circuit 41 for 10 secondsto the liquid crystal cell 38 having the large pretilt angle domains 32h, 35 h which were formed on the alignment films 32, 35 as describedearlier. The transition from the splay alignment state to the bendalignment state or to the twisted bend alignment state (this state isalso hereinafter referred to as “bend alignment state”) was seen in allthe pixels irrespective of the presence or absence of the spacer 51 intheir neighborhood. After application of voltage had been repeated inthe same way, good repeatability was found in the occurrence of thetransition. The reason for such smooth transition is that a core of thetransition is first created in the large pretilt angle domains 32 h, 35h and then, the transition region grows and expands from this core.

[0086] [Embodiment 2]

[0087] In lieu of the polyimide surface alignment agent capable offorming a pretilt angle of about 15° used in Embodiment 1, a polyimidesurface alignment agent of the prepolymerized type capable of foaming apretilt angle of about 70° produced by Japan Synthetic Rubber Co., Ltd.under the number JALS-204 is used in Embodiment 2, for forming a highpretilt angle. The liquid crystal cell 38 having the large pretilt angledomains 32 h, 35 h formed on the alignment films 32, 35 was prepared and5V was applied for 2 seconds to the liquid crystal cell 38. After that,the transition occurred without fail. When a small amount of surfacealignment agent that forms a substantially homeotropic structure ofaround 90° was added, the transition readily occurred with low drivingvoltage.

[0088] [Embodiment 3]

[0089] Another method for forming the large pretilt angle domains 32 h,35 h similar to those in Embodiment 2 will be explained.

[0090] (1) First, a polyimide surface alignment agent of theprepolymerized type capable of forming a pretilt angle of about 5°produced by Japan Synthetic Rubber Co., Ltd. under the number JALS-212is applied to the transparent pixel electrodes 31 and the counterelectrode 34. Then, the product is dried and sintered to form thealignment films 32, 35.

[0091] (2) A polyimide surface alignment agent of the prepolymerizedtype capable of forming a pretilt angle of 70° and commerciallyavailable from Japan Synthetic Rubber Co., Ltd. under the numberJALS-204 is printed on the alignment films 32, 35 at the positionscorresponding to the transparent pixel electrodes 31 such that printedareas each having a diameter of about 10 μm are arranged at a pitch of100 μm. Then, the product is dried and sintered to form the largepretilt angle domains 32 h, 35 h.

[0092] (3) Surface treatment is applied in the same way as described inthe process (2) of Embodiment 1.

[0093] After a voltage of 5V had been applied for one second to theliquid crystal cell 38 having the large pretilt angle regions 32 h, 35 hthus formed on the alignment films 32, 35, the transition occurredwithout fail.

[0094] In Embodiments 1 to 3 described above, the mixing ratio of thesurface alignment agent for producing a large pretilt angle to thesurface alignment agent for producing a small pretilt angle and thediameters of the large pretilt angle domains 32 h, 35 h, are not limitedto the above figures but may be determined in accordance with thevoltage and time required for the transition and with the liquid crystalmaterial used. However, it should be noted that at least one largepretilt angle domain must be formed for every pixel. Transition is morelikely to occur with the greater large pretilt angle and with the biggerdifference between the large pretilt angle and the small pretilt angle.For this reason, the large pretilt angle may be in the range of from 15°to 90° and more preferably from 70° to 90°, while the difference betweenthe larger pretilt angle and the small pretilt angle may be 10° or more.These ranges are, of course, not limitative of the large and smallpretilt angles, which may be determined according to the aboveconditions.

[0095] [Embodiment 4]

[0096] There will be explained another liquid crystal display device inwhich the transition from the splay alignment state to the bendalignment state smoothly occurs. In the following embodiments, elementshaving functions similar to those of Embodiment 1 are designated by thesame reference numerals given to the elements of Embodiment 1 and thedescription of them is omitted. AS seen from FIG. 6, a square-poleprojection 52 is formed on each of the transparent pixel electrodes 31.The height and one side of the cross-section of each square-poleprojection 52 are 4 μm. These projections 52 are formed from an acrylicphotosensitive polymer. It should be noted that the height of theprojections 52 is exaggeratedly illustrated in FIG. 6. The projections52 can be easily formed for example through exposure and development,using corresponding masks. An alignment film 32 is formed over thesurface of each transparent pixel electrode 31 and over the surface ofeach projection 52. This alignment film 32 is formed by application,drying, sintering and surface treatment by use of a low pretilt angleforming surface alignment agent, like the preparation of ordinaryalignment films.

[0097] A voltage of 3V was applied for one second to the liquid crystalcell 38 having the above projections 52 and it was found that thetransition occurred on all the transparent pixel electrodes 31 withoutfail. The occurrence of the transition on all the pixel electrodes 31 isconceivably due to the fact that the liquid crystal molecules in thevicinity of each projection 52 are aligned in a virtually uprightfashion along the surface of the projection 52, forming a core and atransition area grows and expands from this core.

[0098] It should be noted the projection 52 is not limited to the shape,size, material and manufacturing method mentioned above, but at leastone projection 52 should be formed on each transparent pixel electrode31 For instance, the projections 52 may be cylindrical, conical,spherical, pyramidal or prismatic, and are lower than the spacers 51 inheight. To eliminate the need for the spacers 51, the projections 52 maybe equal to the spacers 51 in diameter.

[0099] [Embodiment 5]

[0100] This embodiment provides one example of the liquid crystaldisplay devices, in which a chiral agent is added to the liquid crystal37 to cause the smooth transition from the splay alignment state to thebend alignment state.

[0101] Eleven liquid crystal display devices A1 to A11 (see FIG.

[0102] 7) were prepared, which were designed similarly to the displaydevice of Embodiment 1 except for the following points.

[0103] (a) The large pretilt angle domains 32 h, 35 h are not formed onthe alignment films 32, 35.

[0104] (b) A polyimide surface alignment agent of the prepolymerizedtype capable of forming a pretilt angle of about 5° and produced byJapan Synthetic Rubber Co., Ltd. under the number JALS-212 is used forforming the alignment films 32, 35.

[0105] (c) The spacers S1 are disposed at positions where thetransparent pixel electrodes 31 do not lie.

[0106] (d) Cholesteryl nonanoate serving as a left-handed chiral agentis added to a nematic liquid crystal having positive dielectricanisotropy so that the chiral pitches of the liquid crystal 37 of thedevices A1 to A11 are as indicated in the following Table 1. TABLE 1chiral time required for liquid pitch of observation result uniformtransition crystal liquid of transition at to bend alignment displaycrystal the time of voltage state device (μm) application (second A1  5transition locally 1 occurs and expands A2  7 uniform transition 0occurs across surface with transmissivity variation A3 10 the same asabove 0 A4 20 the same as above 0 A5 40 the same as above 0 A6 60transition locally 1 occurs and quickly expands A7 80 the same as above1 A8 100  transition locally 3 occurs and gradually expands A9 120  thesame as above 60  A10 140  the same as above 120  A11 ∞ the same asabove 600 

[0107] A rectangular wave voltage (frequency=30 Hz, maximum voltage 3V)was applied to the liquid crystal display devices A to A11 respectively.The transition between the alignment states and the time required forcausing uniform transition to the bend alignment state over the entiresurface of each pixel were observed. The result of the observation isdemonstrated in Table 1.

[0108] As seen from Table 1, in the liquid crystal display devices A2 toA5 of chiral pitches from 7 μm to 40 μm (i.e., 7 μm≦ chiral pitch≦40μm), transmission changed instantly across the surface of each pixel andno alignment defects were found. That is, the transition from the splayalignment state to the bend alignment state is thought to have takenplace smoothly.

[0109] In the liquid crystal display devices A1 (chiral pitch=5 μm), A6to A8 (60 μm≦chiral pitch≦100 μm) , the transition locally occurred andexpanded in a considerably short time. In other words, the transitionoccurred across the surface of each pixel with a comparatively smallamount of electric energy.

[0110] In the liquid crystal display devices A9 to A11 (120 μm≦chiralpitch ≦∞) , the transition first occurred locally, and voltage had beenapplied for a long time (1 to 10 minutes) before the transition occurredacross the surface of each pixel. This means that a large amount ofelectric energy was need to cause the transition throughout the pixelsurface.

[0111] It will be understood from the result that the electric energyrequired for the transition from the splay alignment state to the bendalignment state can be reduced and such transition can be carried outwithout fail, by adding a chiral agent to the liquid crystal 37 toimpart a twist component to the liquid crystal 37 and to achieve achiral pitch of 5 to 100 μm, and, more preferably, 7 to 40 μm.

[0112] [Embodiment 6]

[0113] This embodiment provides a liquid crystal display device in whicha chiral agent is added to the liquid crystal 37 employed in Embodiment2. More specifically, cholesteryl nonanoate serving as a left-handedchiral agent is added to the liquid crystal 37 to attain a chiral pitchof 50 μm in this embodiment. Like Embodiment 2, the liquid crystal cell38 having the large pretilt angle domains 32 h, 35 h is designed tocontain the above liquid crystal 37 between the transparent substrates33, 36. The spacers 51 are disposed at positions where the transparentpixel electrodes 31 do not lie.

[0114] A rectangular wave voltage (frequency=30 Hz, maximum voltage=3V)was applied to the above liquid crystal display device having the liquidcrystal cell 38. Then, the transition to the bend alignment state andthe time required for attaining the uniform transition across thesurface of each pixel were observed. The transition firstly occurred inthe large pretilt angle domains 32 h, 35 h and then expanded in aconsiderably short times say, in one second over the entire surface ofeach pixel. This means that the uniform transition across the pixelsurface could be achieved by a relatively small amount of electricenergy. It is understood from the observation that a core for thetransition was first created in the large pretilt angle domains 32 h, 35h and the transition was promoted by the addition of the chiral agent tothe liquid crystal 37 so that the splay alignment state was changed to Sthe bend alignment state very quickly.

[0115] It should be noted that the same inventive effect can be obtainedby adding a chiral agent to the liquid crystal 37 of the liquid crystaldisplay device of Embodiment 1 or Embodiment 3. The pretilt angle may beselected from a wide range as described in Embodiment 3. While thespacers 51 are disposed at positions where the transparent pixelelectrodes 31 do not lie for the sake of observation in Embodiment 5 andEmbodiment 6, they may be placed at position where the transparent pixelelectrodes 31 are disposed.

[0116] [Embodiment 7]

[0117] This embodiment relates to a liquid crystal display device whichdoes not need the transition between the alignment states required bythe OCB mode. That is, the liquid crystal display device of thisembodiment is not an OCB liquid crystal display device, but capable ofproviding response as fast as the OCB mode by virtue of the alignmentcondition similar to that of the OCB mode and its mechanism. As seenfrom FIG. 8, the physical structure of the liquid crystal display deviceof this embodiment is similar to that of Embodiment 5 (see FIG. 7), butdiffers from the. latter in the directors of the alignment films 32, 35as shown in FIG. 9. Specifically, the twist angle w of the liquidcrystal molecules of this embodiment is 180°.

[0118] The liquid crystal display device of Embodiment 7 is fabricatedin the following procedure.

[0119] (1) Two transparent substrates 33, 36 made of glass and havingthe transparent pixel electrodes 31 and the counter electrode 34respectively are coated with a polyamic acid type polyimide surfacealignment agent RN-474 produced by Nissan Chemical Industries Ltd. byspin coating. Then, the coating material is cured at 180° within athermostatic chamber over one hour, thereby preparing the alignmentfilms 32, 35.

[0120] (2) The alignment films 32, 35 are rubbed with a rayon rubbingcloth in the direction indicated in FIG. 9 so as to produce a twistangle a of 180°

[0121] (3) The spacers 51 produced by Sekisui Fine Chemical Co., Ltd.are interposed between the transparent substrates 33, 36 so as to createa gap distance of 6 μm between the substrates 33, 36. These substrates33, 36 are then bonded by use of Structbond 352A (sealing resin)produced by Mitsui Toatsu Chemical Co., Ltd., thereby forming the liquidcrystal cell 38.

[0122] (4) Cholesteryl nonanoate serving as a left-handed chiral agentis added to the positive nematic liquid crystal material ZLI-2411 (NIpoint=65°, Δ=0.140) produced by Merck KGaA to produce the liquid crystal37.

[0123] (5) The liquid crystal 37 is injected into the gap between thetransparent substrates 33, 36 placed in an evacuated chamber and thensealed.

[0124] (6) The polarizing plates 39, 40 and the phase compensator 43(=bi-axial phase-different film) having a retardation of 50 nm arebonded to the liquid crystal cell 38 such that they are oriented asshown in FIG. 9, thereby fabricating the liquid crystal display device.

[0125]FIG. 10 shows the result of a measurement of thevoltage-transmission characteristic of the liquid crystal display devicefabricated in the above procedure. In the measurement, a rectangularwave having a frequency of 30 Hz was applied to the liquid crystaldisplay device with a known method. It is understood from FIG. 10 thatthe change in the alignment of the liquid crystal molecules is continualand an alignment state similar to the bend alignment state can beobtained smoothly and reliably. When displaying images with appliedvoltages of 1.8V to 6V, the contrast ratio is 230:1.

[0126] Table 2 shows the sum of response times when the applied voltageis changed from V1 to V2 and when the applied voltage is changed from V2to V1. It is understood from Table 2 that fast response can be obtainedwhen changing applied voltage between two levels corresponding twohalftones which have a slight difference in brightness. TABLE 2 V1 → V2→ V1 V1 (V) V2 (V) sum of response times (msec) 1.8 2.4 31 2.4 3.0 293.0 3.6 26 3.6 4.2 25 4.2 4.8 26 4.8 5.4 23 5.4 6.0 21

[0127] The operational condition of this liquid crystal display deviceis as follows. When no voltage is applied to the device, the alignmentof the liquid crystal molecules is the same as that of the STN (Supertwisted Nematic) mode because the alignment films 32, 35 are conditionedso as to produce a twist angle ω of 180°. When a voltage of 1.8V (withwhich transmission becomes maximal as shown in FIG. 10) or more isapplied to the device, the alignment of the liquid crystal moleculesbecomes similar to that of the OCB mode. Therefore, fast response asindicated above can be obtained. Even when the above voltage is appliedto the device, the liquid crystal molecules are kept in the twistedcondition so that discrete phase transition such as. the transition fromthe splay alignment state to the bend alignment state as seen in the OCBmode will never occur. This permits image displaying just afterapplication of voltage.

[0128] According to the liquid crystal display device of Embodiment 7,as the liquid crystal molecules are in the twisted condition asdescribed above, the polarizing plates 39, 40 may be disposed with theirpolarizing axes being parallel to each other (i.e., parallel nicol)instead of the 10 cross nicol-arrangement where the polarizing axescross at right angles as shown in FIG. 9. In this case, normally blackdisplay is carried out. Specifically, the brightness of display imagesdecreases as the applied voltage decreases. It should be noted that thephase difference of the phase compensator 43 needs to be selectedaccording to the arrangement of the polarizing axes, because theappropriate value of phase difference when the polarizing axes cross atright angles differs from that when the polarizing axes are parallel toeach other.

[0129] [Embodiment 8]

[0130] The liquid crystal display device of Embodiment 8 has the samestructure as that of Embodiment 7 but differs from the latterprincipally in the twist angle ω of the liquid crystal molecules.

[0131] Seven liquid crystal display devices B1 to B7 were fabricated,which have the same structure as the liquid crystal display device ofEmbodiment 7 except for the following points.

[0132] (a) As the liquid crystal 37, a positive nematic liquid crystalZLI-2293 (NI point=85°, Δ=0.140) commercially available from Merck KGaAis used. As a left-handed chiral agent, cholesteryl nonanoate is used toproduce a chiral pitch of 10 μm.

[0133] (b) The thickness of the liquid crystal layer is 5 μm.

[0134] (c) The phase compensator 43 employed in Embodiment 7 is notused.

[0135] (d) The twist angle ω of each device is as shown in Table 3.TABLE 3 liquid crystal twist angle of response time display deviceliquid crystal (msec) B1 150 41 B2 160 28 B3 170 27 B4 180 23 B5 190 27B6 200 29 B7 210 40

[0136]FIG. 11 shows the voltage-transmission characteristic of each ofthe liquid crystal display devices B1 to B7 when measured at roomtemperature. Table 3 demonstrates the sum of response times when theapplied voltage is changed from V1 to V2 and when the applied voltage ischanged from V2 to V1 in the case of each device, the values of V1 andV2 for each device being shown in Table 4. For example, in the case ofthe device B1, the sum is obtained by adding the response time when theapplied voltage is changed from 3.1V to 4.1V to the response time whenthe applied voltage is changed from 4.1V to 3.1V. TABLE 4 liquid crystaldisplay device V1 (V) V2 (V) B7 2.3 3.3 B6 2.4 3.4 B5 2.5 3.5 B4 2.6 3.6B3 2.8 3.8 B2 3.0 4.0 B1 3.1 4.1

[0137] As seen from Table 3, in each case, fast response can be obtainedby applying a voltage higher than the voltage that causes the maximalvalue of transmission, with the twist angle K being in the range of from160° to 200°. When the twist angle ω falls in the above range, themovement of the liquid crystal molecules is little disturbed by thebackflow caused by application of voltage, so that response as fast asthat of the OCB mode can be achieved.

[0138] Although the phase compensator 43 is not provided in thisembodiment, the phase compensator 43 suited for each liquid crystaldisplay device may be employed to obtain higher contrast display image.The brightness characteristics when viewing each device squarely can beadjusted by optimizing the phase difference Δnd of the liquid crystalcell 38 when no voltage is applied. While the chiral pitch of the liquidcrystal 37 is twice the thickness of the layer of the liquid crystal 37in this embodiment, it may range from one to three times, because if thechiral pitch is less than the thickness of the layer 37, the twist angleω becomes larger than the desired angle by 180° and if the chiral pitchis more than three times the thickness of the layer 37, the condition ofthe director alignment becomes instable.

[0139] [Embodiment 9]

[0140] This embodiment provides an OCB liquid crystal display devicewhere the transition from the splay alignment state to the bendalignment state is caused continuously and reversibly, by setting thetwist angle ω to 10°. The liquid crystal display device of Embodiment 9is an OCB liquid crystal display device similar to that of Embodiment 5,but differs from the latter in that the twist angle ω of the liquidcrystal molecules is 10° as indicated in FIG. 12.

[0141] The liquid crystal display device of Embodiment 9 is fabricatedin the same procedure as Embodiment 7 but different from the latter inthe following points.

[0142] (a) A prepolymerized type polyimide surface alignment agentAL-5062 produced by Japan Synthetic Rubber Co., Ltd. is used as thealignment films 32, 35.

[0143] (b) The alignment films 32, 35 are rubbed in the direction shownin FIG. 12 to produce a twist angle ω of 10°

[0144] (c) The transparent substrates 33, 36 are bonded with a gapdistance of 7 μm.

[0145] (d) A positive nematic liquid crystal material LIXON-5052 (NIpoint=104°, Δn=0.102) produced by Chisso Corporation which does notcontain a chiral agent is used as the liquid crystal 37.

[0146] (e) The phase compensator 43, which has a phase difference of 45nm when observed in a normal direction and is composed of a uniaxialfilm and a biaxial film bonded to each other, is bonded as shown in FIG.12.

[0147] A rectangular wave having a frequency of 30 Hz was applied by aknown method to the liquid crystal display device fabricated under theabove conditions and then the voltage-transmission characteristic of thedevice was measured. FIG. 13 shows the result of the measurement. Theliquid crystal molecules were in the splay alignment state with novoltage applied to the device, but they were brought into the bendalignment state when the applied voltage was in the vicinity of about2.3V. It was confirmed from the observation that the change in thealignment of the liquid crystal molecules at that time was continual andreversible and the transition to the bend alignment state was smoothlyperformed without fail. When image displaying was performed with appliedvoltages from 2.3V to 10V, the contrast ratio was 315:1. The sum of theresponse times when changing the applied voltage from 2.3V to 2.8V andwhen changing vice versa was 22 msec. Thus, fast response could beobtained when changing applied voltage between two levels correspondingtwo halftones which have a slight difference in brightness.Additionally, faster response was observed when driving the device witha large driving voltage amplitude.

[0148] As described above, the liquid crystal display device of thisembodiment is an OCB liquid crystal display device in which twistingpower is given to the alignment of the liquid crystal. With thisarrangement, the transition from the splay alignment state to the bendalignment state can be carried with excellent reliability andrepeatability so that it finds a wide range of applications.

[0149] [Embodiment 10]

[0150] This embodiment provides a bend mode liquid crystal displaydevice which has improved viewing angles in various directions withoutuse of the phase compensator 43. As seen from FIG. 14, the mechanicalstructure of this liquid crystal display device is similar to thestructure of the device of Embodiment 5 (see FIG. 7) except for thefollowing points. (a) For fabricating the alignment films 32, 35, adifferent material is used (described later). (b) The alignment films32, 35 are respectively divided into two domains. (c) There is notprovided the phase compensator 43. (d) The gap distance between thetransparent substrates 33, 36 is 8 μm. (e) The liquid crystal 37 doesnot contain a chiral agent.

[0151] Next, the division of the alignment films 32, 35 will bedescribed in detail. As shown in FIG. 15, the alignment films 32, 35formed on the transparent substrates 33, 36 are divided into two domains32 a, 32 b and domains 35 a, 35 b respectively, at the regionscorresponding to the transparent pixel electrodes 31. The alignmentfilms 32, 35 are conditioned so as to form a bend director alignment inwhich the liquid crystal molecules contacting the opposed pairs ofdomains 32 a, 35 a lie in the plane including X and Z axes whereas theliquid crystal molecules contacting the opposed pairs of domains 32 b,35 b lie in the plane including Y and Z axes. More specifically, thedomains 32 a, 35 a are conditioned such that the director fieldproximate to them has a pretilt angle of about 5° with respect to Xaxis, while the domains 32 b, 35 b are conditioned such that thedirector field proximate to them has a pretilt angle of about 5° withrespect to Y axis.

[0152] The above alignment films 32, 35 are formed and conditioned inthe following way.

[0153] (1) A prepolymerized-type, polyimide surface alignment agent(e.g., AL-0656 produced by Japan Synthetic Rubber Co., Ltd.) is appliedto the transparent pixel electrodes 31 and the counter electrode 34,dried and sintered, thereby forming the alignment films 32, 35.

[0154] (2) The entire surfaces of the alignment films 32, 35 are rubbedwith a rubbing cloth made of rayon so that the liquid crystal moleculeson the surface of the alignment films 32, 35 form a pretilt angle ofabout 5° with respect to Y axis.

[0155] (3) Masking is carried out utilizing the photolithographictechnique such that only the domains 32 a, 35 a of the alignment films32, 35 are exposed.

[0156] (4) Rubbing is done with a rayon rubbing cloth similarly to thestep (2) such that only the domains 32 a, 35 a form a pretilt angle ofabout 5° with respect to X axis.

[0157] In the liquid crystal cell 38 thus formed, a rectangular wavevoltage (amplitude=3V, frequency=30 Hz) was applied between thetransparent pixel electrodes 31 and the counter electrode 34 by thedriver circuit 41. Then, the condition of the director alignment of theliquid crystal 37 was observed with a polarization microscope. It wasfound that, there are formed, in the liquid crystal 37 contacting thealignment film 32 formed on the transparent pixel electrodes 31, (i) thebend director field oriented in the direction of X axis and proximate tothe domain 32 a and (ii) the bend director field oriented in thedirection of Y axis and proximate to the domain 32 b, these differentlyoriented director fields being separated by a disclination line 42.

[0158] The plates 39, 40 were disposed on both sides of the liquidcrystal cell 38 respectively. A specified image signal voltage wasapplied between the transparent pixel electrodes 31 and the counterelectrode 34, and viewing angles in various planes perpendicular to thedisplaying plane were checked utilizing back light or reflection light.The same large viewing angle characteristics (e.g., about ±55° ) wereobtained in the plane including X and Z axes and in the plane includingY and Z axes. The substantially similar viewing angle characteristicswere found in other planes than the above planes. This means that theliquid crystal display device of Embodiment 10 is capable of displayingimages which are highly bright, well-contrasted and free from gray scaleinversion, when viewed from various directions.

[0159] [Embodiment 11]

[0160] In addition to the optical elements employed in Embodiment 10,there may be provided the negative-type, phase compensator 43 foroptical compensation between the transparent substrate 36 and thepolarizing plate 40 as shown in FIG. 16. The use of the phasecompensator 43 permits a further improvement in viewing angles (forexample, about ±60°) and a reduction in the driving voltage. The phasecompensator 43 may be provided between the transparent substrate 33 andthe polarizing plate 39 instead of providing it between the transparentsubstrate 36 and the polarizing plate 40, or alternatively provided atboth positions.

[0161] [Embodiment 12]

[0162] The surface treatment for the alignment films 32, 35 may becarried out in the following way.

[0163] (1) Like the step (1) of Embodiment 10, a surface alignment agent(e.g., PI-610 produced by Nissan Chemical Industries Ltd.) is applied tothe transparent pixel electrodes 31 and the counter electrode 34, driedand then sintered to form the alignment films 32, 35.

[0164] (2) As shown in FIG. 17, ultraviolet light (wavelength 365 nm,energy density=4.5 mW/cm², polarizing direction=the direction of Y-axis)is directed in the direction of arrow A (i.e., at about 45° with respectto X axis in the plane including X and Z axes) onto the position(corresponding to the domain 32 a to be formed) of the alignment film 32for 10 minutes so that the liquid crystal molecules near the surface ofthe alignment film 32 in this position are aligned at a pretilt angle ofabout 5. relative to X axis.

[0165] (3) Similarly to the above step (2), ultraviolet light(polarizing direction=the direction of X axis) is directed in thedirection of arrow B onto the position (corresponding to the domain 32 bto be formed) of the alignment film 32 so that the liquid crystalmolecules near the surface of the alignment film 32 in this position arealigned at a pretilt angle of about 5° relative to Y axis.

[0166] (4) Similarly to the steps (2) and (3), ultraviolet light isdirected in the directions of arrow C-and arrow D onto the positions(corresponding to the domains 35 a, 35 b to be formed) of the alignmentfilm 35, respectively so that the liquid crystal molecules near thesurface of the alignment film 35 in these positions are aligned atpretilt angles, symmetrically to the director fields of the domains 32a, 32 b of the alignment film 32 respectively.

[0167] The director fields may be formed in the plane including X and Zaxes as well as in the plane including Y and Z axes like Embodiment 10,by the above-described radiation of ultraviolet lights having differentpolarizing directions and different radiating directions. In addition,this technique provides the advantages that it can facilitate uniformsurface treatment and that it avoids a possible decrease in yield whichwould be caused by damage to the alignment films due tophotolithography. In consequence, highly improved stability of directoralignment can be achieved.

[0168] The radiating conditions, radiating directions and polarizingdirections of ultraviolet light are not limited to those described abovebut may be varied according to the materials of the liquid crystal 37and the alignment films 32, 35. Further, the surface treatment maycomprise not only the above-described radiation of ultraviolet light butalso rubbing carried out prior to and/or after the radiation step. Itshould be noted that the surface treatment of this embodiment may beapplied to other embodiments.

[0169] While Embodiments 10 to 12 have been described with cases wherethe alignment films are respectively divided into two domains whichcauses two director fields in planes crossing at right angles, otherways of division may be possible. For example, the films arerespectively divided into a plurality of domains to form a plurality ofdirector fields so that viewing angles in various directions can beimproved. The domains do not necessarily have the same size but may bevaried in size according to the viewing angle characteristics. Thetransition from the initial director alignment state to the bendalignment state at the time of a start of voltage application may bespeeded up by adding an appropriate amount of chiral agent (e.g.,cholesteryl nonanoate) to the liquid crystal 37, so that the speed ofresponse can be increased. In this case, although the bend directoralignment of the liquid crystal 37 includes twist, the same effect onviewing angles can be achieved.

[0170] [Embodiment 13]

[0171] This embodiment provides a liquid crystal display device whichdoes not require, unlike the OCB mode, use of a phase compensator northe arrangement in which the polarizing plate is disposed with itspolarizing axis being oriented in a direction different from theconditioning direction of the alignment films. The liquid crystaldisplay device of Embodiment 13 is similar to the OCB mode in terms ofthe alignment condition, but has the same principle as the Guest-hostmode (hereinafter referred to as “GHI” mode) has in terms of reproducinglight levels.

[0172]FIG. 18 illustrates a cross section of a liquid crystal displaydevice C according to Embodiment 13 of the invention. The liquid crystaldisplay device C is a light-transmissive type liquid crystal displaydevice made up of a liquid crystal cell 110 and a polarizing plate 109disposed on the light incoming side of the liquid crystal cell 110, theliquid crystal cell 110 comprising a pair of glass substrates 101, 108between which a liquid crystal layer 105 is sandwiched. The innersurfaces of the glass substrates 101, 108 are respectively provided withtransparent electrodes 102, 107. Disposed on the inner surfaces of thetransparent electrodes 102, 107 are alignment films 103, 106. Thepolarizing plate 109 is arranged such that its polarizing axis issubstantially parallel to the direction of the longitudinal axis of theliquid crystal molecules proximate to the interface of the glasssubstrate 108 which is positioned on the light incoming side.

[0173] The liquid crystal cell 110 is a twisted liquid cell in which theliquid crystal molecules of the liquid crystal layer 105 are twistedbetween the glass substrates 101. 108. In this embodiment, the twistangle a (see FIG. 19) of the liquid crystal layer 105 is 180°. Theliquid crystal layer 105 contains a black dye in addition to a liquidcrystal material. The black dye is a dichromatic dye such as an azoxydye or anthraquinone dye and is of the so-called posi-type which exertsa significant absorbing effect on a light polarized in a directionparallel to the longitudinal axis of liquid crystal molecules and asmall absorbing effect on a light polarized in a direction parallel tothe lateral axis of liquid crystal molecules. The liquid crystal of theliquid crystal layer 105 is preformed so as to have a chiral pitch of 12μm by adding a chiral agent. The liquid crystal display device C isdesigned to keep a gap distance of 6 μm between the substrates by use ofspacers 104.

[0174] The liquid crystal display device C having the above structure ismanufactured by the following fabrication method.

[0175] (1) A polyamic acid type polyimide surface alignment agent RN-474produced by Nissan Chemical Industries Ltd. is applied by spin coatingto the two glass substrates 101, 108 having the transparent electrodes102, 107. The agent is cured at 180° C. over one hour in a thermostaticchamber.

[0176] (2) The coated substrates are rubbed in the direction shown inFIG. 19 using a rayon rubbing cloth. Note that, in FIG. 19, referencenumeral 121 designates the rubbing direction of the substrate 101 on thelight outgoing side, reference numeral 122 the rubbing direction of thesubstrate 108 on the light incoming side, and reference numeral 123 thedirection of the polarizing axis of the polarizing plate 109. Since thetwist angle ω is 180° in Embodiment 13, the rubbing direction 121 of theglass substrate 101 is the same as the rubbing direction 122 of theglass substrate 108.

[0177] (3) The glass substrates 101, 108 are bonded such as to produce agap distance of 6 μm therebetween using the spacers 104 produced bySekisui Fine Chemical Co., Ltd. and Structbond 352A (the commercial nameof a sealing resin produced by Mitsui Toatsu Chemical Co., Ltd.),whereby the vacant liquid crystal cell 110 is prepared.

[0178] (4) 100 parts by weight of a positive nematic liquid crystalmaterial ZLI-2411 commercially available from Merck KGaA (Nematicisotropic transition point (NI point)=65°, anisotropy of refractiveindex (Δn)=0.140) is mixed with 1 part by weight of a black dye S-466produced by Mitsubishi Chemical Corporation. Note that the liquidcrystal ZLI-2411 contains cholesteryl nonanoate as a left-handed chiralagent and has a chiral pitch of 12 μm. The liquid crystal thus preparedis injected into the vacant, liquid crystal cell 110 placed in anevacuated chamber.

[0179] (5) The polarizing plate 109 is bonded to the liquid crystal cell110 such that the rubbing direction 122 of the glass substrate 108 iscoincident with the direction of the polarizing axis 123 of thepolarizing plate 109, as shown in FIG. 19.

[0180] The voltage-brightness characteristic of the liquid crystaldisplay device C was measured while a rectangular wave voltage of 30 Hzbeing applied to it. The result of the measurement is shown in FIGS. 20and 21. It should be noted that FIG. 21 is a partially enlarged diagramcorresponding to FIG. 20. As clearly seen from FIG. 20, thevoltage-brightness characteristic of the liquid crystal display device Cis outlined as follows: the brightness level is substantially zero whenno voltage is applied and is maintained at approximately zero from thetime voltage application starts to the time the applied voltage reachesa Freedericksz threshold voltage V_(th). After that, the brightnesslevel increases as the applied voltage increases.

[0181] The above voltage-brightness characteristic is attributed to thefollowing fact. When the applied voltage is equal to or less than theFreedericksz threshold V_(th), the liquid crystal molecules are parallelto the substrates and the molecules of the black dye are constrained bythe liquid crystal molecules, so that the longitudinal axis of the dyemolecules is parallel to the substrates. Therefore, an incident light125 which has passed through the polarizing plate 109 is mostly absorbedby the black dye so that the brightness level becomes substantiallyzero. In the range where the applied voltage is equal to or more thanthe Freedericksz threshold voltage V_(th), the liquid crystal moleculescomparatively close to the center of the liquid crystal cell risevertically relative to the substrates. As the applied voltage increases,the liquid crystal molecules closer to the substrates rise substantiallyvertically. Under the influence of the movement of the liquid crystalmolecules, the dye molecules also vertically rise toward the substrates.This causes a decrease in the light absorption effect of the black dye,so that the level of brightness increases.

[0182] According to the voltage-brightness characteristic of the liquidcrystal display device C, the level of brightness gently increases witha first gradient just after the voltage applied to the liquid crystalcell 110 exceeds the Freedericksz threshold voltage V_(th), and then itfurther increases with a second gradient sharper than the first oneafter the applied voltage exceeds about 2.5V. This is obvious from FIGS.24 and 25 to be described later. In the first voltage range from thepoint the applied voltage exceeds the Freedericksz threshold voltageV_(th) to the point the applied voltage reaches 2.5V, a big change isnot seen in the tilt angle and orientation of the liquid crystalmolecules. After the applied voltage exceeds 2.5V, the tilt angle andorientation vary significantly. Therefore, the molecules of the blackdye affected by the movement of the liquid crystal molecules have littlefluctuation in the first voltage range and fluctuate considerably afterthe applied voltage exceeds 2.5V. As a result, the light absorbabilityof the black dye declines to a large extent in the second stage comparedto the prior stage, resulting in a sharp increase in brightness.

[0183] The main feature of the liquid crystal display device of thisembodiment resides in that image displaying is performed with voltagesin the high voltage range which are higher than the turning point, i.e.,2.5V at which brightness changes abruptly in the voltage-brightnesscharacteristic curve. It is confirmed by the following test result thatthe liquid crystal display device C achieves fast response and a highcontrast ratio in gray scale displaying.

[0184] We first measured the brightness of display images in the liquidcrystal display device C, with the applied voltage ranging from 2.5V to11.0V and calculated the contrast ratio. As a result, it was confirmedthat a contrast ratio of 136:1 was obtained which was good enough forgray scale displaying.

[0185] Then, the voltage applied to the liquid crystal display device Cwas changed from 2.5V to 3.7V, 4.9V, 6.1V, 7.3V, 8.5V, 9.7V and 10.9Vsequentially, and the rise time and fall time of each change weremeasured to obtain the sum of these times. The respective sums for thevoltage changes were 43 msec, 39 msec, 37 msec, 35 msec, 35 msec, 30msec and 30 msec. The response time of an ordinary liquid crystaldisplay device is known to be as follows: the sum of the rise time andfall time is about 150 msec. when voltage is changed between 2.5V and3.7V, and is 30 to 40 msec. when voltage is changed between 9.7V and10.9V. As obvious from the test result, the liquid crystal displaydevice C has excellent response characteristics

[0186] It is well understood from the foregoing description that theliquid crystal display device C can perform gray scale displaying withfast response, when the driving voltage ranges from 2.5V to 10.9V. Whilethis embodiment has been described with a case where images aredisplayed in 8 tones, the invention is not limited to this and enableshigh-speed image displaying likewise in cases where display images havemore than 8 tones. This is also easily assumed from the above testresult.

[0187] AS described earlier, the liquid crystal display device C ofEmbodiment 13 has a liquid crystal cell having a twist angle ω of 180°in which a guest-host. (GH type) liquid crystal material is injected,and the device C differs from STN liquid crystal display devices in therange of driving voltage and in the way of light propagation. Fastresponse can be ensured in gray scale displaying like the OCB mode, byemploying the above range of driving voltage. Since light transmissionis controlled by controlling the light absorption by the black dye,there is no need to provide an optical compensating layer and black huenever fluctuates visually in this embodiment. Accordingly, the liquidcrystal display device of this embodiment is, in principle, free fromvisual color changes while ensuring response as fast as that of theconventional OCB liquid crystal display devices, so that it finds a widerange of applications.

[0188] Although a black dye is used in this embodiment, dyes/pigments ofother colors may be used according to applications. In cases where ablack dye is used, image displaying may be performed with voltages equalto and less than the Preedericksz threshold voltage V_(th) only whenblack color images are displayed, in order to further decrease thebrightness level of black images.

[0189] For reference, the arrangement of the polarizing plate will beexplained. While the polarizing axis of the polarizing plate issubstantially parallel to the longitudinal axis of the liquid crystalmolecules in the vicinity of the interfaces of the substrates in thisembodiment, it is conceivable that the polarizing axis may be arrangedat a certain angle such as to 20° or 45° relative to the longitudinalaxis. However, such non-parallel arrangement where the polarizing axisand the longitudinal axis of the molecules are not parallel to eachother does not obtain a satisfactory black level, which results in poorimage quality. The reason for this is as follows. In the high voltagerange, the voltage-brightness characteristic in the case of the parallelarrangement where the polarizing axis and the longitudinal axis of themolecules are parallel to each other is, in principle, identical to thevoltage-brightness characteristic in the case of the non-parallelarrangement. However, in the low voltage range, the voltage-brightnesscharacteristic in the case of the parallel arrangement differs from thatin the case of the non-parallel arrangement. More precisely, where thepolarizing axis and the longitudinal axis of the molecules are notparallel, the molecules of the dye are not parallel to the polarizingplate when no voltage is applied and therefore, the absorbed light issmall in amount compared to the case of the parallel arrangement, sothat brightness remains at a certain level Even when the applied voltageslightly exceeds the Freedericksz threshold voltage V_(th), brightnessis maintained at a level substantially similar to the level at the timeof no voltage application. When the applied voltage increases further,the tilt angle and orientation of the liquid crystal molecules have aparticular relationship with the orientation of the polarizing plate andas a result, brightness drops drastically. When the applied voltageincreases still further, brightness increases in conjunction therewith.Even when brightness is at the lowest level, it is not zero but a levelwhich is not low enough to display black color, and therefore, theliquid crystal display device having the non-parallel arrangement failsin ensuring a satisfactory black level, leading to poor image quality.

[0190] A test conducted by us has, however, proved that where thepolarizing plate is placed with its polarizing axis being substantiallyperpendicular to the longitudinal axis of the liquid crystal molecules,the lowest level of brightness is not zero but acceptable for displayingblack color. In consideration of this fact, the polarizing axis of thepolarizing plate may be arranged substantially perpendicular to thelongitudinal axis of the liquid crystal molecules and with suchperpendicular arrangement, image displaying may be done with voltageshigher than the voltage at which brightness is at the lowest level.

[0191] [Embodiment 14]

[0192] Embodiment 14 has the same structure as Embodiment 13 except thatwhile the twist angle ω is 180° in Embodiment 13, the twist angle ω ofEmbodiment 14 is in the range of from 160° to 200° With the structure ofEmbodiment 14, the same inventive effect as that of Embodiment 13 can beobtained. Details will be explained below.

[0193] Seven liquid crystal display devices D1 to D7 were fabricated bythe same method as that of the liquid crystal display device C ofEmbodiment 13 except for the following points.

[0194] (a) As a liquid crystal material, a positive nematic liquidcrystal ZLI-2293 (NI point=85°, Δn=0.140) produced by Merck XGaA andcontaining 1 wt % of a black dye S-466 (produced by Mitsubishi ChemicalCorporation) is used.

[0195] (b) The thickness of the liquid crystal layer is 5 μm and thechiral pitch is 10 μm.

[0196] (c) The twist angle ω of the liquid crystal of each devicediffers from that of Embodiment 13. As seen from Table 5, the twistangle ω of the liquid crystal display devices D1 to D7 are 150°, 160°,170°, 180°, 190°, 200°, and 210° respectively. TABLE 5 liquid crystaltwist angle of display device liquid crystal D1 150 D2 160 D3 170 D4 180D5 190 D6 200 D7 210

[0197] The following test was conducted to measure the response of eachof the liquid crystal display devices D1 to D7. Concretely, the range ofdriving voltage (V1-V2) for each device was determined as shown in Table6. For evaluating the response of each device, the response times whenthe applied voltage was changed from V1 to V2 and when it was changedfrom V2 to V1 were respectively measured, and then the sum of theseresponse times was obtained. Table 7 shows the test result. It should benoted that V1 is the applied voltage when the gradient of thevoltage-brightness characteristic abruptly changes in each of the liquidcrystal display devices D1 to D7. TABLE 6 liquid crystal display deviceV1 (V) V2 (V) D1 2.2 3.1 D2 2.3 3.2 D3 2.4 3.3 D4 2.5 3.4 D5 2.6 3.5 D62.7 3.6 D7 2.8 3.7

[0198] TABLE 7 liquid crystal response time display device (msec) D1 52D2 35 D3 33 D4 31 D5 31 D6 35 D7 57

[0199] As seen from Table 7, while the liquid crystal display devicesD1, D7 exhibit poor response as their response times are more than 50msec., the display devices D2, D3, D4, D5, D6 exhibit rapid response astheir respective response times are less than 40 msec. It is understoodfrom the result that the twist angle, which permits rapid response,ranges from 160° to 200°.

[0200] The reason why rapid response can be obtained when the twistangle falls in the range of from 160° to 200° is as follows. It iswidely known that, in a liquid crystal display device having a twistedliquid crystal cell and a polarizing plate, the response is dependent ofthe angle between the twisted liquid crystal molecules and thepolarizing plate and becomes fast when this angle falls in a certainrange. Under the condition that the polarizing plate is disposed withits polarizing axis being parallel to the liquid crystal molecules inthe interface of the substrate 108 on the light incoming side, the twistangle for obtaining fast response falls in the range of from 160° to200° Accordingly, if the twist angle ranges from 160° to 200°, thedegree to which the movement of the liquid crystal molecules isprevented by the backflow caused by actuation can be restricted as muchas possible so that response as fast as that of the OCB mode can beachieved.

[0201] Regarding the liquid crystal display devices D2, D4, D5, D6 ofthis embodiment, the viewing angle dependence of hues were checked atvarious brightness levels. These devices were found to be virtually freefrom hue shifts so that their usefulness was proved.

[0202] Although the chiral pitch of the liquid crystal material is setto be twice the thickness of the liquid crystal layer in thisembodiment, the preferable range of the chiral pitch is one to threetimes the thickness of the liquid crystal layer. The reason for this isthat if the chiral pitch is smaller than the thickness of the liquidcrystal layer, the twist angle of the liquid crystal layer becomeslarger than the desired value by 180° and if the chiral pitch is morethan three times the thickness of the liquid crystal layer, thecondition of the director alignment tends to be instable.

[0203] [Embodiment 15]

[0204] The liquid crystal display device of Embodiment 15 has the samestructure as that of the liquid crystal display device D of Embodiment14 except that the twist angle ω of the liquid crystal of Embodiment 14ranges from 160° to 200°, whereas the twist angle ω of Embodiment 15ranges from 250° to 290° FIGS. 22 and 23 show the voltage-brightnesscharacteristic of a liquid crystal display device E4 having a twistangle ω of 270°, which is a typical example of Embodiment 15. Note thatFIG. 23 is a partially enlarged view corresponding to FIG. 22.

[0205] It is obvious from FIGS. 22, 23 that the voltage-brightnesscharacteristic of the liquid crystal display device E of this embodimentis essentially identical to that of the liquid crystal display device Chaving a twist angle ω of 180°. One of the features of Embodiment 15resides in that image displaying is performed, similarly to Embodiments13, 14, with driving voltages higher than the point (=3.6V on the curvesshown in FIGS. 22, 23) at which the gradient of the voltage-brightnesscharacteristic curve abruptly changes. It has been experimentallyverified by the test described below that fast response and a highcontrast ratio in gray scale displaying can be achieved in thisembodiment. The test will be concretely described.

[0206] Seven liquid crystal display devices E1 to E7 were fabricated bythe fabrication method that was similar to that of the liquid crystaldisplay device C of Embodiment 13 except for the following points. InEmbodiment 15, a positive nematic liquid crystal ZLI-2293 (NI point=85°,Δn=0.140) produced by Merck KGaA containing 1 wt % of a black dye S-466produced by Mitsubishi Chemical Corporation is used as the liquidcrystal material. The thickness of the liquid crystal layer is 20 μm,and the chiral pitch is 24 μm. Twist angle ω different from that ofembodiment 13 are adapted. Specifically, the twist angles of the liquidcrystals in the liquid crystal display device E1 to E7 are, as shown inTable 8, 240°, 250°, 260 270, 280 , 290 , and 300°, respectively. TABLE8 liquid crystal twist angle of display device liquid crystal E1 240 E2250 E3 260 E4 270 E5 280 E6 290 E7 300

[0207] The range of applied voltage (V1-V2) for each of the displaydevices E1 to E7 is determined as shown in Table 9. Table 10 shows thesum of the response times when the applied voltage is changed from V1 toV2 and when it is changed vice versa-in each device. It should be notedV1 is the applied voltage when the gradient of the voltage-brightnesscharacteristic abruptly changes in each of the liquid crystal displaydevices E1 to E7. TABLE 9 liquid crystal display device V1 (V) V2 (V) E13.2 3.9 E2 3.3 4.0 E3 3.4 4.1 E4 3.5 4.2 E5 3.6 4.3 E6 3.7 4.4 E7 3.84.5

[0208] TABLE 10 liqiud crystal response time display device (msec)contrast ratio E1 69  70:1 E2 50 120:1 E3 43 170:1 E4 37 196:1 E5 44180:1 E6 48 135:1 E7 62  85:1

[0209] The twist angle and the thickness of the liquid crystal layer ofEmbodiment 15 are large. Therefore, as seen from Table 10, Embodiment 15is somewhat poor in response characteristics compared to Embodiment 14,but acceptable for practical use. Further, when image displaying isperformed with voltages higher than those shown in Table 9,substantially similar response characteristics can be obtained inoperation for changing applied voltage between two levels correspondingtwo halftones which have a slight difference in brightness.

[0210] For the liquid crystal display device E4, the contrast ratio wasdefined as the ratio of the brightness when 11.0V was applied to thebrightness when 3.0V was applied. The value of this contrast ratio wasfound to be 196. For other liquid crystal display devices E1 to E3 andE5 to E7, the contrast ratio was likewise defined and their respectivevalues were obtained. Table 10 demonstrates the contrast ratio of eachdevice. As seen from Table 10, a contrast and response characteristicsgood enough for practical use can be obtained with a twist angle rangingfrom 250° to 290°. The response when the twist angle is in the range offrom 250° to 290° is better than those when it is 240° and when it is300° for the same reason that the twist angle ranging from 160° to 200°achieves good response. A high contrast can be obtained when the twistangle is in the range of from 250° to 290° for the following reason.Where the twist angle exceeds 290°, the twist angle is so large that thelight propagation within the liquid crystal layer cannot follow thetwist, which entails a loss of light and, in consequence, a poorcontrast.

[0211] The viewing angle dependence of hues at various brightness levelswas observed in the liquid crystal display devices E2 to E6 andvirtually no hue fluctuation was observed. This proves the usefulness ofthese display devices E2 to E6.

[0212] While the chiral pitch of the liquid crystal material in thisembodiment is 1.2 times the thickness of the liquid crystal layer, thepreferable range may be one to twice the thickness of the liquid crystallayer. The reason for this is that if the chiral pitch is smaller thanthe thickness of the liquid crystal layer, the twist angle of the liquidcrystal layer becomes 180° larger than the desired value and if thechiral pitch is more than twice the thickness of the liquid Crystallayer, the twist angle of the liquid crystal layer becomes 180° smallerthan the desired value.

[0213] [Embodiment 16]

[0214] While Embodiments 13 to 15 determine the range of driving voltagefor the liquid crystal display device from the voltage-brightnesscharacteristic, this range is determined from the average tilt angle ofthe liquid crystal molecules in Embodiment 16. Brightness usually variesaccording to the variation of the voltage applied to the liquid crystaldisplay device and this fact is attributable to changes in the tiltangle of dye molecules following changes in the tilt angle of the liquidcrystal molecules. For this reason, the range of driving voltage may bedetermined not only from the voltage-brightness characteristic but alsofrom the average tilt angle of the liquid crystal molecules. Thisembodiment provides one example in which the range of driving voltagefor the liquid crystal display device is determined from the averagetilt angle of the liquid crystal molecules.

[0215] This embodiment will be concretely explained. The directordistribution of the liquid crystal display device C of Embodiment 13 wascalculated. The applied voltage was varied by 1V from 0V to 10V. FIGS.24 to 25 show the result of the test. Note that FIG. 24 shows the tiltangle of the liquid crystal molecules in relation to the substrateplane, whereas FIG. 25 shows the orientation of director alignment. InFIG. 24, line X0 represents a case where a voltage of 0V was applied.Similarly, lines X1, X2, X3, X4, XS, X6, X7, X8, X9 and X10 representcases where the applied voltage was 1V, 2V, 3V, 4V, 5V, 6V, 7V, 8V, 9Vand 10V, respectively. Referring to FIG. 25, line Y0 represents a casewhere the applied voltage was 0V, and likewise, lines Y1, Y2, Y3, Y4,Y5, Y6, Y7, Y8, Y9 and Y10 represent cases where the applied voltage was1V, 2V, 3V, 4V, 5V, 6V, 7V, 8V, 9V and 10V, respectively.

[0216] It is understood from FIGS. 24, 25 that the tilt angle of theliquid crystal molecules and the orientation of director alignmentchange slightly when the applied voltage was up to 2V, and changegreatly when the applied voltage was equal to or more than 3V. It isconceivable that due to the changes in the tilt angle and the directoralignment orientation, which correspond to changes in the appliedvoltage, the gradient of brightness levels largely changes in thevicinity of 2.5V in the voltage-brightness characteristic of the liquidcrystal display device C (see FIG. 21). Accordingly, the same range ofapplied voltage determined by the voltage-brightness characteristic canbe obtained through determination using the average tilt angle of theliquid crystal molecules. We calculated the average tilt angle of theliquid crystal molecules for each value of applied voltage. FIG. 26shows the result. It is understood from FIGS. 20, 26 that the averagetilt angle of the liquid crystal molecules corresponding to an appliedvoltage of 2.5V is 10°. Thus, in a liquid crystal display device havinga twist angle ranging from 160° to 200°, image displaying is possiblycarried out when the average tilt angle of the liquid crystal moleculesis 10° or more. When the average tilt angle is less than 10° neithersatisfactory brightness nor a practicable contrast ratio can beobtained.

[0217] [Embodiment 17]

[0218] While Embodiment 16 determines the range of driving voltage fromthe average tilt angle in the liquid crystal display device whose twistangle ω ranges from 160° to 200°, Embodiment 17 carries out the drivingvoltage range determination with the average tilt angle in the liquidcrystal display device whose twist angle ω ranges from 250° to 290°. Itwas experimentally proven that Embodiment 17 had the same inventiveeffect of Embodiment 16.

[0219] This embodiment will be concretely explained. The directorconfiguration of the liquid crystal display device E4 prepared accordingto Embodiment 15 was obtained through calculation, while the appliedvoltage being changed by 1V from 0 to 10V. FIGS. 27 and 28 show theresult of the calculation for each voltage value. FIG. 27 shows the tiltangle of the liquid crystal molecules relative to the substrate plane,whereas FIG. 28 shows the orientation of director alignment. FIG. 29shows the average tilt angle of the liquid crystal moleculescorresponding to each applied voltage value. It is understood from FIGS.22, 29 that the average tilt angle of the liquid crystal moleculescorresponding to an applied voltage of 3.6V is 20°. Accordingly, in thecase of the liquid crystal display device whose twist angle is 250° to290°, image displaying is possible when the average tilt angle of theliquid crystal molecules is 20° or more. When the average tilt angle isless than 20°, satisfactory black color displaying cannot be performed,and a practicable contrast ratio cannot be obtained.

[0220] [Embodiment 18]

[0221] While Embodiments 13 to 17 use a twisted liquid crystal cell,Embodiment 18 is characterized by a splay liquid crystal cell having atwist angle ω of 0° The liquid crystal display device F of Embodiment 18has the same structure as the liquid crystal display device C ofEmbodiment 13, except that the liquid crystal display device F has aliquid crystal cell formed by adding a black dye in the conventional OCBmode liquid crystal cell and that the polarizing plate is disposed withits polarizing axis being substantially parallel to-the rubbingdirection of the substrates. Another difference is that the liquidcrystal display device F does not incorporate the birefringence modeemployed in the conventional OCB liquid crystal display devices bututilizes the Guest-host mode. The liquid crystal display device F ofEmbodiment 18 is fabricated in the following method.

[0222] (1) A prepolymerized type polyimide surface alignment agentAL-5062 produced by Japan Synthetic Rubber Co., Ltd. is applied by spincoating to the two glass substrates 101, 108 having the transparentelectrodes 102, 107, and then cured at 180° over one hour within athermostatic chamber.

[0223] (2) then, the surfaces of the coated substrates are rubbed in thedirection shown in FIG. 30, using a rayon rubbing cloth. Referring toFIG. 30, reference numeral 121 represents the rubbing direction of thesubstrate 101 positioned on the light outgoing side, reference numeral122 the rubbing direction of the substrate 108 positioned on the lightincoming side, and reference numeral 123 the direction of the polarizingaxis of the polarizing plate 109. In Embodiment 18, the rubbingdirection 121 of the substrate 101 is the same as the rubbing direction122 of the glass substrate 108 in order to produce a twist angle ω of 0°

[0224] (3) The substrates 101, 108 are bonded so as to have a gapdistance of 14 μm therebetween by use of the spacers 104 produced bySekisui Fine Chemical Co., Ltd. and Structbond 352A (sealing resin)produced by Mitsui Toatsu Chemical Co., Ltd., whereby the vacant liquidcrystal cell 110 is formed.

[0225] (4) 100 parts by weight of a positive nematic liquid crystalLIXON-5052 (NI point=104°, Δn=0.102) produced by Chisso Corporation andcontaining no chiral agent and 1 part by weight of a black dye S-466produced by Mitsubishi Chemical Corporation are injected in the vacantliquid crystal cell 110 placed in an evacuated chamber.

[0226] (5) The polarizing plate 109 is bonded to the liquid crystal cell110 such that the rubbing directions 121, 122 of the substrates coincidewith the direction 123 of the polarizing axis of the polarizing plate asshown in FIG. 30, thereby fabricating the liquid crystal display deviceF.

[0227] The voltage-brightness characteristic of the liquid crystaldisplay device F thus fabricated was measured by a known method while arectangular wave voltage of 30 Hz being applied to it. The result of themeasurement is shown in FIG. 31. When no voltage was applied, thedirector alignment of the liquid crystal layer was in the splayalignment state, but when the applied voltage was in the vicinity ofabout 2.3V, the director alignment was brought into the bend alignmentstate. Referring to FIG. 31, when image displaying was done with adriving voltage of 1.8V to 12V, the contrast ratio was 80:1. The sum ofthe rise time and fall time when the voltage was changed from 2.3V to2.8V was 30 msec.

[0228]FIG. 32 shows the range of viewing angles when the brightnessratio (i.e., contrast ratio) is more than 5:1 with driving voltages of10V and 1.8V. As seen from FIG. 32, the liquid crystal display device Fof this embodiment has good viewing angle characteristics, providing aviewing angle of more than 120° in a vertical direction and a viewingangle of 160° in a lateral direction. Therefore, the liquid crystaldisplay device F proved itself very valuable in practical use. Whenchecking the viewing angle dependence of the displaying characteristicsduring actuation of the liquid crystal display device F with drivingvoltages ranging from 2V to 8V, gray scale inversion was not recognized.

[0229] As has been described above, Embodiment 18 uses a splay liquidcrystal cell in which the liquid crystal layer can be brought into thebend alignment state by voltage application and uses a dye contained inthe liquid crystal layer, so that it presents several advantages. First,it ensures fast response equal to that of the OCB mode as well as goodviewing angle characteristics. Second, it overcomes the viewing angledependence of the hues of display images that has been one of theoutstanding problems suffered by the conventional OCB liquid crystaldisplay devices employing the birefringence mode. In addition, since thedevice F is not the birefringence mode, there is no need to include aphase compensator layer

[0230] Although voltages equal to and lower than the Freederickszthreshold voltage are applied only when displaying black-color images inthis embodiment, black-color displaying may be done with voltages higherthan 2.3V (see FIG. 31) if there is not strong requirement for a highcontrast.

[0231] [Embodiment 19]

[0232]FIG. 33 shows a cross section of a liquid crystal display deviceaccording to Embodiment 19 of the invention. The liquid crystal displaydevice G of this embodiment is a light reflective-type liquid crystaldisplay device having a reflector 140. In FIG. 33, elements having thesame functions as those of the elements of the liquid crystal displaydevice F shown in FIG. 18 are designated by the same reference numeralsgiven to the elements of the device F. Essentially, the liquid crystaldisplay device G is fabricated by incorporating the reflector 140 in thestructure of the device F of Embodiment 18. However, the device Gdiffers from the device F of Embodiment 18 in that the liquid crystallayer 105 contains a chiral agent. Use of a chiral agent permits thesmooth transition from the initial state of the liquid crystal moleculesto a twisted, bend alignment state and increases response speed. In thiscase, the director alignment of the liquid crystal is in the bendalignment state having twist that exists at the center of the liquidcrystal, but the inventive effect of Embodiment 18 in terms of viewingangles can be achieved by Embodiment 19.

[0233] The fabrication method of the liquid crystal display device Ghaving the above features is as follows.

[0234] (1) A prepolymerized-type polyimide surface alignment agentAL-5062 produced by Japan Synthetic Rubber Co., Ltd. is applied by spincoating to the two glass substrates 101, 108 having the transparentelectrodes 102, 107, and then cured at 180° over one hour within athermostatic chamber.

[0235] (2) Then, the surfaces of the coated, glass substrates 101, 108are rubbed in the same direction, using a rayon rubbing cloth to producea twist angle ω of 0°. The glass substrates 101, 108 are bonded so as tohave a gap distance of 104m therebetween by use of the spacers 104produced by Sekisui Fine Chemical Co., Ltd. and Structbond 352A that isa sealing resin produced by Mitsui Toatsu Chemicals Co. Ltd., wherebythe vacant liquid crystal cell 110 is fored.

[0236] (3) 100 parts by weight of a positive nematic liquid crystalLIXON-5052 (NI point=104° , Δn=0.102) produced by Chisso Corporation andhaving a chiral pitch of 20 μm and 1 part by weight of a black dye S-466produced by Mitsubishi Chemical Corporation are injected in the vacantliquid crystal cell 110 placed in an evacuated chamber.

[0237] (4) The polarizing plate 109 is bonded to the liquid crystal cell110 such that the rubbing direction of the substrates coincides with thedirection of the polarizing axis of the polarizing plate, and thereflector 140 is bonded to the liquid crystal cell 110, therebyfabricating the liquid crystal display device G.

[0238] The voltage-brightness characteristic of the liquid crystaldisplay device G thus fabricated was measured by a known method while arectangular wave voltage of 30 Hz being applied to it. The contrastratio obtained when the display device G was viewed squarely was 30:1.

[0239] When displaying images in 8 tones in the liquid crystal displaydevice G, the response between every two tones was 30 msec or less, andthe viewing angle dependence of hues was not observed. To obtain therange of viewing angles with which a contrast ratio of 5:1 or more canbe obtained, a measurement was conducted like Embodiment 18. It wasfound that the display device G had a wide range of viewing angles,providing a viewing angle of 100° in a vertical direction and a viewingangle of 115° in a lateral direction. The usefulness of the displaydevice G was thus confirmed. It should be noted that while thepolarizing plate 109 is disposed on the light incoming side of theliquid crystal cell 110 in Embodiments 13 to 19, it may be disposed onthe light outgoing side.

[0240] [Embodiment 20]

[0241] This embodiment provides a liquid crystal display deviceincorporating the OCB mode or a similar mode, that is designed tocompensate the different transmission characteristics of the threeprimary colors. Such compensation is accomplished by employing differentpretilt angles for the three primary colors, instead of adjustingapplied voltage for every primary color.

[0242] Concretely, the pretilt angle is so varied as to hold therelationship described by: the pretilt angle for blue < the pretiltangle for green < the pretilt angle for red. That is, the pretilt anglecorresponding to blue is the smallest among three. If the pretilt angleis made too small, the energy necessary for the transition from thesplay alignment state to the bend alignment state increases, so that thetransition becomes difficult to carry out. Therefore, it is necessary toset the pretilt angle for blue in a range that causes the transitionwith ease. Red has the largest pretilt angle and if the pretilt angle ismade too large, it will impair displaying with the appropriate benddirector alignment. Therefore, the pretilt angle for red should be nomore than around 30°. There must be a preferable range for the pretiltangle for each primary color, blue, green and red, to satisfy the aboveconditions.

[0243] There will be explained on a surface treatment technique forproducing the director alignment having different pretilt angles for thethree primary colors.

[0244] (1) First, a polyamic acid type polyimide alignment filmPSI-A2204 produced by Chisso Corporation is applied using a spinner tothe entire surfaces of the electrodes formed on the substrates and then,cured.

[0245] (2) For forming a pretilt angle for red, application of anegative resist OMR-83 produced by Tokyo Ohka Kogyo Co., Ltd. exposureby use of a photo mask and development are sequentially carried out,such that only the region corresponding to red pixels is exposed. Inthis condition, a homeotropic agent (produced by Merck KGaA) is diluted,applied to and chemically combined to the surface of the red region.

[0246] By such application of the homeotropic agent, the pretilt angleof only the region to which the agent has been applied can be madelarger than those of other regions, when the cell is filled with aliquid crystal in the later step.

[0247] (3) After removing the resist, the surfaces of the electrodes areentirely rubbed by the ordinary method.

[0248] (4) For forming a pretilt angle for blue, only the bluepixel-corresponding region is exposed to radiation of an ultraviolet rayof 360 nm, using a photo mask. The radiation of the ultraviolet raycauses decomposition of the alignment film so that when the cell isfilled with a liquid crystal later, the pretilt angle of only thisregion can be made smaller.

[0249] When the above surface treatment is carried out, various pretiltangles can be obtained by adjusting the dilution rate of the homeotropicagent, the radiation energy of ultraviolet light and others. In anactual liquid crystal display device formed by the foregoing technique,the pretilt angle of the blue pixel-corresponding region on the upperand lower substrates is about 2° and the pretilt angle of the redpixel-corresponding region on both substrates is about 19°. The pretiltangle of the green-pixel corresponding region on both substrates towhich no special treatment has been applied is about 5° to 6° like thecase of the prior art liquid crystal display devices.

[0250]FIG. 34 shows the transmission-applied voltage characteristic ofthe liquid crystal display device of Embodiment 20. As understood fromFIG. 34, the virtually same transmission can be obtained for each of theprimary colors, blue, green, red, irrespective of applied voltage. Withthis arrangement, voltage adjustment for the three primary colors is nolonger necessary, and image displaying with appropriate hues is enabledwithout loosing a balance even if the same voltage is applied to theregions of different colors. Although Embodiment 20 does not use a phasecompensator, it may be included in Embodiment 20 in which case, the sameinventive effect can be obtained.

[0251] While Embodiment 19 has been described with a reflective liquidcrystal display device, Embodiment 19 is applicable to transmissiveliquid crystal display devices having no reflector. Also, otherembodiments described earlier are applicable to both reflective andtransmissive liquid crystal display devices. In the case of a reflectiveliquid crystal display device, the substrates may be made of silicon orreflective materials such as metals including aluminum, or alternativelya reflective metal film may be applied to either the pixel electrodes orthe counter electrode.

[0252] All of the above-described embodiments may be applied to passivematrix-type liquid crystal-display devices and also to activematrix-type liquid crystal display devices incorporating an activeelement such as a TFT (Thin Film Transistor) or MIM (Metal InsulatedMetal) formed on either substrate. The active matrix-type enablesdisplay images of better quality. The invention is applicable to varioustypes of liquid crystal display devices such as normally-white liquidcrystal display devices and normally-black liquid crystal displaydevices which display white and black images respectively, when novoltage is applied.

[0253] It should be noticed that the materials of the elementsconstituting each device are not limited to those described above. Forexample, plastic substrates may be used as the transparent substratesand other surface alignment agents than polyimide surface alignmentagents may be used. While left-handed cholesteryl nonanoate is used asthe chiral agent in the foregoing embodiments, other types of chiralagents including the left-handed and right-handed may be used. As amatter of course, the pretilt angle and the gap distance between thetransparent substrates are not limited to the above values, but may bevaried according to the material of the liquid crystal and other opticaldesign conditions. Although it is preferable that the pretilt angles ofthe alignment films on both sides of the liquid crystal cell be equal toeach other in view of the symmetry of viewing angles, they may differfrom each other in order to facilitate a change in the alignment stateof the liquid crystal molecules.

[0254] Further, in Embodiment 1 and other embodiments, a phasecompensator is provided on only one side of the liquid crystal cell butboth sides may be respectively provided with a phase compensator.

What is claimed is:
 1. A liquid crystal display device comprising (1) apixel electrode, (2) a counter electrode and (3) a liquid crystalenclosed between the pixel and counter electrodes, wherein therespective opposed surfaces of the pixel and counter electrodes areconditioned such that liquid crystal molecules contacting or in thevicinity of said surfaces have specified pretilt angles, wherein imagesare displayed by changing light transmission through formation of a bendalignment state of the liquid crystal, and wherein a large pretilt angledomain is formed on at least either one of said surfaces of the pixeland counter electrodes, the large pretilt angle domain causing a largerpretilt angle of liquid crystal molecules than a region surrounding thelarge pretilt angle domain does.
 2. A liquid crystal display deviceaccording to claim 1, wherein the pretilt angle of the liquid crystalmolecules caused by the large pretilt angle domain is 10° or more largerthan that caused by the surrounding region.
 3. A liquid crystal displaydevice according to claim 1, wherein the pretilt angle of the liquidcrystal molecules caused by the large pretilt angle domain is 15° ormore.
 4. A liquid crystal display device according to claim 3, whereinthe pretilt angle of the liquid crystal molecules caused by the largepretilt angle domain is 70° or more.
 5. A liquid crystal display deviceaccording to claim 1, wherein a plurality of said pixel electrodes areprovided and at least one large pretilt angle domain is formed on eachpixel electrode.
 6. A liquid crystal display device according to claim1, wherein said large pretilt angle domain-is formed by a surfacealignment agent which causes a larger pretilt angle of the liquidcrystal molecules than the surrounding region does.
 7. A liquid crystaldisplay device according to claim 1, wherein said large pretilt angledomain is formed by a projection which causes a larger pretilt angle ofthe liquid crystal molecules than the surrounding region does.
 8. Aliquid crystal display device according to claim 1, wherein said liquidcrystal contains a chiral agent.
 9. A method for fabricating a liquidcrystal display device which comprises (1) a pixel electrode, (2) acounter electrode and (3) a liquid crystal enclosed between the pixeland counter electrodes and wherein images are displayed by changinglight transmission through formation of a bend alignment state of theliquid crystal, said method comprising the steps of: (a) forming a filmmade from a mixture of a first surface alignment agent and a secondsurface alignment agent on at least one of the surfaces of said pixeland counter electrodes, the first surface alignment agent causing afirst pretilt angle of liquid crystal molecules in the vicinity of saidpixel electrode or counter electrode, the second surface alignment agentcausing a second pretilt angle larger than the first pretilt angle, and(b) causing the phase separation of said first and second surfacealignment agents contained in said film.
 10. A method for fabricating aliquid crystal display device which comprises (1) a pixel electrode, (2)a counter electrode and (3) a liquid crystal enclosed between the pixeland counter electrodes and wherein images are displayed by changinglight transmission through formation of a bend alignment state of theliquid crystal, said method comprising the steps of: (a) forming analignment film made from a first surface alignment agent on at least oneof the surfaces of said pixel and counter electrodes, the first surfacealignment agent causing a first pretilt angle of liquid crystalmolecules in the vicinity of said pixel electrode or counter electrode,and (b) partially forming an alignment film made from a second surfacealignment agent on the alignment film made from the first surfacealignment agent, the second surface alignment agent causing a secondpretilt angle larger than the first pretilt angle.
 11. A liquid crystaldisplay device comprising (1) a pixel electrode, (2) a counterelectrode, (3) a liquid crystal enclosed between the pixel and counterelectrodes, and (4) a phase compensating layer, wherein images aredisplayed by changing light transmission through formation of a bendalignment state of the liquid crystal, and wherein said liquid crystalcontains a chiral agent.
 12. A liquid crystal display device accordingto claim 11, wherein said chiral agent produces a chiral pitch in saidliquid crystal, said chiral pitch ranging from 5 μm to 100 μm.
 13. Aliquid crystal display device according to claim 11, wherein said chiralagent produces a chiral pitch in said liquid crystal, said chiral pitchranging from 7 μm to 40 μm.
 14. A liquid crystal display devicecomprising (1) a first substrate having a pixel electrode formedthereon, (2) a second substrate having a counter electrode formedthereon and positioned opposite the first substrate, (3) a liquidcrystal enclosed between the first and second substrates, (4) a firstpolarizer and a second polarizer disposed so as to sandwich the firstand second substrates, the polarizing axes of the first and secondpolarizers crossing at right angles, and (5) a driver circuit forapplying driving voltage between the pixel electrode and the counterelectrode, wherein the liquid crystal molecules of said liquid crystalhave a twist angle ranging from 160° to 200°, and wherein said drivercircuit applies driving voltage between the pixel and counterelectrodes, the driving voltage being higher than the highest one ofvoltages that cause the maximal value of light transmission in thedriving voltage-transmission characteristic of the liquid crystaldisplay device.
 15. A liquid crystal display device comprising (1) afirst substrate having a pixel electrode formed thereon, (2) a secondsubstrate having a counter electrode formed thereon and positionedopposite the first substrate, (3) a liquid crystal enclosed between thefirst and second substrates, (4) a first polarizer and a secondpolarizer disposed so as to sandwich the first and second substrates,the polarizing axes of the first and second polarizers being parallel toeach other, and (5) a driver circuit for applying driving voltagebetween the pixel electrode and the counter electrode, wherein theliquid crystal molecules of said liquid crystal have a twist angleranging from 160° to 200°, and wherein said driver circuit appliesdriving voltage between the pixel and counter electrodes, the drivingvoltage being higher than the highest one of voltages that cause theminimal value of light transmission in the driving voltage-transmissioncharacteristic of the liquid crystal display device.
 16. A liquidcrystal display device according to claim 14 or 15, further comprising aphase compensating layer at least either between the first substrate andthe first polarizer or between the second substrate and the secondpolarizer.
 17. A liquid crystal display device according to claim 16,wherein said phase compensating layer is a biaxial phase compensatingfilm.
 18. A liquid crystal display device according to claim 16, whereinsaid phase compensating layer is a laminated film composed of a biaxialphase compensating film and a uniaxial phase compensating film.
 19. Aliquid crystal display device according to claim 14 or 15, wherein thechiral pitch of said liquid crystal is not less than the thickness ofthe liquid crystal and not more than three times the thickness of theliquid crystal.
 20. A liquid crystal display device comprising (1) apixel electrode, (2) a counter electrode and (3) a liquid crystalenclosed between the pixel and counter electrodes, wherein images aredisplayed by changing light transmission through formation of a bendalignment state of the liquid crystal, and wherein pixels correspondingto the pixel electrode are divided into at least two domains which causebend director fields having different orientations in the liquidcrystal.
 21. A liquid crystal display device according to claim 20,wherein the orientations of the bend director fields caused by the twodomains cross at right angles.
 22. A liquid crystal display deviceaccording to claim 20, wherein the pixel electrode and the counterelectrode are respectively provided with an alignment film at theirsurfaces facing the liquid crystal, and wherein each alignment film isdivided into said domains which are conditioned so as to causedifferently oriented director fields in the liquid crystal.
 23. A liquidcrystal display device according to claim 22, wherein the pairs ofopposed domains, one domain of each pair being formed on the alignmentfilm of the pixel electrode and the other domain of each pair beingformed on the alignment film of the counter electrode, are conditionedsuch that each pair of opposed domains form a pair of director fields,the director fields of each pair respectively including liquid crystalmolecules aligned at pretilt angles in a plane perpendicular to adisplaying plane such that the director fields of each pair aresymmetric with respect to a plane that is parallel to the displayingplane and located in the middle of the distance between the pixelelectrode and the counter electrode.
 24. A liquid crystal display deviceaccording to claim 20, further comprising a phase compensating layerformed on at least either the outer surface of the pixel electrode orthe outer surface of the counter electrode, for optically compensatingthe director alignment of the liquid crystal molecules.
 25. A liquidcrystal display device according to claim 20, wherein said liquidcrystal contains a chiral agent.
 26. A method for fabricating a liquidcrystal display device, wherein images are displayed by changing lighttransmission through formation of a bend alignment state of a liquidcrystal enclosed between a pixel electrode and a counter electrode, andwherein alignment films are respectively formed on the surfaces of thepixel electrode and the counter electrode, the surfaces facing theliquid crystal, the alignment film on the pixel electrode and a portionof the alignment film on the counter electrode which portion correspondsto the pixel electrode being respectively divided into at least twodomains having different conditioning directions by directingultraviolet lights to two regions corresponding to the two domains to beformed, the ultraviolet lights being directed in different directions orhaving different polarizing directions.
 27. A liquid crystal displaydevice comprising (1) a twisted liquid crystal cell having a liquidcrystal layer sandwiched between a pair of substrates, the liquidcrystal layer having liquid crystal molecules twisted between said pairof substrates and (2) a polarizing plate disposed on either the lightincoming side or light outgoing side of the liquid crystal cell, whereinsaid polarizing plate is disposed such that its polarizing axis issubstantially parallel to the longitudinal axis of the liquid crystalmolecules on the interface of one of said pair of substrates, saidsubstrate being on the light incoming side or light outgoing side,wherein the twist angle of the liquid crystal molecules in said liquidcrystal layer is in the range of from 160° to 200° and said liquidcrystal layer contains a dye or pigment, which has a voltage-brightnesscharacteristic according to which when the voltage applied to saidliquid crystal cell exceeds the Freedericksz threshold voltage of theliquid crystal, brightness first rises gently with a first gradient andthen rises with a second gradient sharper than the first gradient, andwhich performs image displaying with driving voltages at least higherthan the voltage corresponding to the turning point where brightnesschanges from the first gradient to the second gradient.
 28. A liquidcrystal display device comprising (1) a twisted liquid crystal cellhaving a liquid crystal layer sandwiched between a pair of substrates,the liquid crystal layer having liquid crystal molecules twisted betweensaid pair of substrates and (2) a polarizing plate disposed on eitherthe light incoming side or light outgoing side of the liquid crystalcell, wherein said polarizing plate is disposed such that its polarizingaxis is substantially parallel to the longitudinal axis of the liquidcrystal molecules on the interface of one S of said pair of substrates,said substrate being on the light incoming side or light outgoing side,wherein the twist angle of the liquid crystal molecules in said liquidcrystal layer is in the range of from 250° to 290° and said liquidcrystal layer contains a dye or pigment, which has a voltage-brightnesscharacteristic according to which when the voltage applied to saidliquid crystal cell exceeds the Freedericksz threshold voltage of theliquid crystal, brightness first rises gently with a first gradient andthen rises with a second gradient sharper than the first gradient, andwhich performs image displaying with driving voltages at least higherthan the voltage corresponding to the turning point where brightnesschanges from the first gradient to the second gradient.
 29. A liquidcrystal display device comprising (1) a twisted liquid crystal cellhaving a liquid crystal layer sandwiched between a pair of substrates,the liquid crystal layer having liquid crystal molecules twisted betweensaid pair of substrates and (2) a polarizing plate disposed on eitherthe light incoming side or light outgoing side of the liquid crystalcell, wherein said polarizing plate is disposed such that its polarizingaxis is substantially parallel to the longitudinal axis of the liquidcrystal molecules on the interface of one of said pair of substrates,said substrate being on the light incoming side or light outgoing side,wherein the twist angle of the liquid crystal molecules in said liquidcrystal layer is in the range of from 160° to 200° and said liquidcrystal layer contains a dye or pigment, which performs image displayingwith driving voltages which permit the average tilt angle of liquidcrystal directors relative to the plane of the substrates to be 10° ormore.
 30. A liquid crystal display device comprising (1) a twistedliquid crystal cell having a liquid crystal layer sandwiched between apair of substrates, the liquid crystal layer having liquid crystalmolecules twisted between said pair of substrates and (2) a polarizingplate disposed on either the light incoming side or light outgoing sideof the liquid crystal cell, wherein said polarizing plate is disposedsuch that its polarizing axis is substantially parallel to thelongitudinal axis of the liquid crystal molecules on the interface ofone of said pair of substrates, said substrate being on the lightincoming side or light outgoing side, wherein the twist angle of theliquid crystal molecules in said liquid crystal layer is in the range offrom 250° to 290° and said liquid crystal layer contains a dye orpigment, which performs image displaying with driving voltages whichpermit the average tilt angle of liquid crystal directors relative tothe plane of the substrates to be 20° or more.
 31. A liquid crystaldisplay device according to any one of claims 27 to 30, wherein said dyeor pigment is black in color and image displaying is performed withdriving voltages equal to and less than the Freedericksz thresholdvoltage of the liquid crystal only when black images are displayed. 32.A liquid crystal display device comprising (1) a liquid crystal cellhaving a liquid crystal layer sandwiched between a pair of substrateswhich are rubbed in the same direction and (2) a polarizing platedisposed on either the light incoming side or light outgoing side of theliquid crystal cell, wherein said polarizing plate is disposed with itspolarizing axis being substantially parallel to the rubbing direction ofsaid substrates, wherein said liquid crystal layer contains a dye orpigment, and wherein said liquid crystal cell is a bend directoralignment cell in which a bend alignment state is formed at the time ofapplication of voltage.
 33. A liquid crystal display device according toclaim 32, wherein the bend alignment state formed at the time ofapplication of voltage includes twist at the center of the liquidcrystal cell.
 34. A liquid crystal display device according to claims33, wherein said liquid crystal contains a chiral agent.
 35. A liquidcrystal display device comprising (1) a plurality of pixel electrodesconstituting a plurality of pixels, (2) a counter electrode, (3) aliquid crystal enclosed between the pixel electrodes and the counterelectrode, and (4) a color filter having regions respectivelycorresponding to said pixels, each region transmitting any one of aplurality of colors, wherein at least either the surfaces of the pixelelectrodes or the surface of the counter electrode is conditioned suchthat liquid crystal molecules in the vicinity of the surfaces or surfaceare aligned so as to form specified pretilt angles, wherein images aredisplayed by changing light transmission through formation of a bendalignment state of said liquid crystal, and wherein said specifiedpretilt angles vary according to the colors of the pixels.
 36. A liquidcrystal display device according to claim 35, wherein said specifiedpretilt angles are determined such that when the same voltage is appliedbetween the pixel electrodes for different colors and the counterelectrode, the same transmission can be obtained for the pixels ofdifferent colors.